Remove a useless feature gateing

With the planned lazy TAIT system, this will not really make sense anymore anyway.

src/test/ui/type-alias-impl-trait/issue-60371.rs

@@ -11,7 +11,6 @@ impl Bug for &() {
     //~^ ERROR the trait bound `(): Bug` is not satisfied
 
     const FUN: fn() -> Self::Item = || ();
-    //~^ ERROR type alias impl trait is not permitted here
 }
 
 fn main() {}

src/test/ui/type-alias-impl-trait/issue-60371.stderr

@@ -7,15 +7,6 @@ LL |     type Item = impl Bug;
    = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
    = help: add `#![feature(type_alias_impl_trait)]` to the crate attributes to enable
 
-error[E0658]: type alias impl trait is not permitted here
-  --> $DIR/issue-60371.rs:13:40
-   |
-LL |     const FUN: fn() -> Self::Item = || ();
-   |                                        ^
-   |
-   = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
-   = help: add `#![feature(type_alias_impl_trait)]` to the crate attributes to enable
-
 error[E0277]: the trait bound `(): Bug` is not satisfied
   --> $DIR/issue-60371.rs:10:17
    |
@@ -25,7 +16,7 @@ LL |     type Item = impl Bug;
    = help: the following implementations were found:
              <&() as Bug>
 
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
 Some errors have detailed explanations: E0277, E0658.
 For more information about an error, try `rustc --explain E0277`.

src/test/ui/type-alias-impl-trait/issue-65679-inst-opaque-ty-from-val-twice.rs

@@ -1,4 +1,5 @@
 // compile-flags: -Zsave-analysis
+// check-pass
 
 #![feature(type_alias_impl_trait, rustc_attrs)]
 
@@ -11,9 +12,7 @@ type T = impl Sized;
 
 fn take(_: fn() -> T) {}
 
-#[rustc_error]
 fn main() {
-    //~^ ERROR fatal error triggered by #[rustc_error]
     take(|| {});
     take(|| {});
 }

src/test/ui/type-alias-impl-trait/issue-65679-inst-opaque-ty-from-val-twice.stderr

@@ -1,8 +0,0 @@
-error: fatal error triggered by #[rustc_error]
-  --> $DIR/issue-65679-inst-opaque-ty-from-val-twice.rs:15:1
-   |
-LL | fn main() {
-   | ^^^^^^^^^
-
-error: aborting due to previous error
-