Remove unused static_assert macro

compiler/rustc_data_structures/src/macros.rs

@@ -1,15 +1,3 @@
-/// A simple static assertion macro.
-#[macro_export]
-#[allow_internal_unstable(type_ascription)]
-macro_rules! static_assert {
-    ($test:expr) => {
-        // Use the bool to access an array such that if the bool is false, the access
-        // is out-of-bounds.
-        #[allow(dead_code)]
-        const _: () = [()][!($test: bool) as usize];
-    };
-}
-
 /// Type size assertion. The first argument is a type and the second argument is its expected size.
 #[macro_export]
 macro_rules! static_assert_size {