add_retag: fix comment that does not match the code

compiler/rustc_mir_transform/src/add_retag.rs

@@ -118,7 +118,7 @@ impl<'tcx> MirPass<'tcx> for AddRetag {
         }
 
         // PART 3
-        // Add retag after assignments where data "enters" this function: the RHS is behind a deref and the LHS is not.
+        // Add retag after assignments.
         for block_data in basic_blocks {
             // We want to insert statements as we iterate. To this end, we
             // iterate backwards using indices.