Remove feature gate from let else suggestion

The let else suggestion added by 0d92752b8a
does not need a feature gate any more.

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -491,8 +491,8 @@ impl<'p, 'tcx> MatchVisitor<'_, 'p, 'tcx> {
                     err.span_suggestion_verbose(
                         semi_span.shrink_to_lo(),
                         &format!(
-                            "alternatively, on nightly, you might want to use \
-                             `#![feature(let_else)]` to handle the variant{} that {} matched",
+                            "alternatively, you might want to use \
+                             let else to handle the variant{} that {} matched",
                             pluralize!(witnesses.len()),
                             match witnesses.len() {
                                 1 => "isn't",

src/test/ui/empty/empty-never-array.stderr

@@ -18,7 +18,7 @@ help: you might want to use `if let` to ignore the variant that isn't matched
    |
 LL |     let u = if let Helper::U(u) = Helper::T(t, []) { u } else { todo!() };
    |     ++++++++++                                     ++++++++++++++++++++++
-help: alternatively, on nightly, you might want to use `#![feature(let_else)]` to handle the variant that isn't matched
+help: alternatively, you might want to use let else to handle the variant that isn't matched
    |
 LL |     let Helper::U(u) = Helper::T(t, []) else { todo!() };
    |                                         ++++++++++++++++

src/test/ui/error-codes/E0005.stderr

@@ -19,7 +19,7 @@ help: you might want to use `if let` to ignore the variant that isn't matched
    |
 LL |     let y = if let Some(y) = x { y } else { todo!() };
    |     ++++++++++                 ++++++++++++++++++++++
-help: alternatively, on nightly, you might want to use `#![feature(let_else)]` to handle the variant that isn't matched
+help: alternatively, you might want to use let else to handle the variant that isn't matched
    |
 LL |     let Some(y) = x else { todo!() };
    |                     ++++++++++++++++

src/test/ui/feature-gates/feature-gate-exhaustive-patterns.stderr

@@ -19,7 +19,7 @@ help: you might want to use `if let` to ignore the variant that isn't matched
    |
 LL |     let _x = if let Ok(_x) = foo() { _x } else { todo!() };
    |     +++++++++++                    +++++++++++++++++++++++
-help: alternatively, on nightly, you might want to use `#![feature(let_else)]` to handle the variant that isn't matched
+help: alternatively, you might want to use let else to handle the variant that isn't matched
    |
 LL |     let Ok(_x) = foo() else { todo!() };
    |                        ++++++++++++++++

src/test/ui/pattern/usefulness/issue-31561.stderr

@@ -21,7 +21,7 @@ help: you might want to use `if let` to ignore the variants that aren't matched
    |
 LL |     let y = if let Thing::Foo(y) = Thing::Foo(1) { y } else { todo!() };
    |     ++++++++++                                   ++++++++++++++++++++++
-help: alternatively, on nightly, you might want to use `#![feature(let_else)]` to handle the variants that aren't matched
+help: alternatively, you might want to use let else to handle the variants that aren't matched
    |
 LL |     let Thing::Foo(y) = Thing::Foo(1) else { todo!() };
    |                                       ++++++++++++++++

src/test/ui/pattern/usefulness/non-exhaustive-defined-here.stderr

@@ -187,7 +187,7 @@ help: you might want to use `if let` to ignore the variant that isn't matched
    |
 LL |     let _x = if let Opt::Some(ref _x) = e { _x } else { todo!() };
    |     +++++++++++                           +++++++++++++++++++++++
-help: alternatively, on nightly, you might want to use `#![feature(let_else)]` to handle the variant that isn't matched
+help: alternatively, you might want to use let else to handle the variant that isn't matched
    |
 LL |     let Opt::Some(ref _x) = e else { todo!() };
    |                               ++++++++++++++++

src/test/ui/recursion/recursive-types-are-not-uninhabited.stderr

@@ -19,7 +19,7 @@ help: you might want to use `if let` to ignore the variant that isn't matched
    |
 LL |     let x = if let Ok(x) = res { x } else { todo!() };
    |     ++++++++++                 ++++++++++++++++++++++
-help: alternatively, on nightly, you might want to use `#![feature(let_else)]` to handle the variant that isn't matched
+help: alternatively, you might want to use let else to handle the variant that isn't matched
    |
 LL |     let Ok(x) = res else { todo!() };
    |                     ++++++++++++++++

src/test/ui/uninhabited/uninhabited-irrefutable.stderr

@@ -18,7 +18,7 @@ help: you might want to use `if let` to ignore the variant that isn't matched
    |
 LL |     let (_y, _z) = if let Foo::D(_y, _z) = x { (_y, _z) } else { todo!() };
    |     +++++++++++++++++                        +++++++++++++++++++++++++++++
-help: alternatively, on nightly, you might want to use `#![feature(let_else)]` to handle the variant that isn't matched
+help: alternatively, you might want to use let else to handle the variant that isn't matched
    |
 LL |     let Foo::D(_y, _z) = x else { todo!() };
    |                            ++++++++++++++++

src/test/ui/uninhabited/uninhabited-matches-feature-gated.stderr

@@ -122,7 +122,7 @@ help: you might want to use `if let` to ignore the variant that isn't matched
    |
 LL |     let x = if let Ok(x) = x { x } else { todo!() };
    |     ++++++++++               ++++++++++++++++++++++
-help: alternatively, on nightly, you might want to use `#![feature(let_else)]` to handle the variant that isn't matched
+help: alternatively, you might want to use let else to handle the variant that isn't matched
    |
 LL |     let Ok(x) = x else { todo!() };
    |                   ++++++++++++++++