Rollup merge of #63333 - jethrogb:jb/error-codes-features, r=Mark-Simulacrum

Remove unnecessary features from compiler error code list

src/librustc_mir/error_codes.rs

@@ -2027,7 +2027,6 @@ fn main() {
 end of the function body. So a reference to them cannot be returned.
 
 ```compile_fail,E0515
-#![feature(nll)]
 fn get_dangling_reference() -> &'static i32 {
     let x = 0;
     &x
@@ -2035,7 +2034,6 @@ fn get_dangling_reference() -> &'static i32 {
 ```
 
 ```compile_fail,E0515
-#![feature(nll)]
 use std::slice::Iter;
 fn get_dangling_iterator<'a>() -> Iter<'a, i32> {
     let v = vec![1, 2, 3];
@@ -2233,7 +2231,6 @@ struct Foo<'a> {
 Example of erroneous code:
 
 ```compile_fail,E0712
-#![feature(nll)]
 #![feature(thread_local)]
 
 #[thread_local]
@@ -2286,8 +2283,6 @@ impl<'a> Drop for S<'a> {
 by reference:
 
 ```
-#![feature(nll)]
-
 pub struct S<'a> { data: &'a mut String }
 
 impl<'a> Drop for S<'a> {
@@ -2312,7 +2307,6 @@ impl<'a> Drop for S<'a> {
 Erroneous code example:
 
 ```compile_fail,E0716
-# #![feature(nll)]
 fn foo() -> i32 { 22 }
 fn bar(x: &i32) -> &i32 { x }
 let p = bar(&foo());