update error codes

Author: lcnr

compiler/rustc_error_codes/src/error_codes/E0730.md

@@ -3,8 +3,6 @@ An array without a fixed length was pattern-matched.
 Erroneous code example:
 
 ```compile_fail,E0730
-#![feature(const_generics)]
-
 fn is_123<const N: usize>(x: [u32; N]) -> bool {
     match x {
         [1, 2, ..] => true, // error: cannot pattern-match on an

compiler/rustc_error_codes/src/error_codes/E0770.md

@@ -10,6 +10,5 @@ fn foo<T, const N: T>() {} // error!
 To fix this error, use a concrete type for the const parameter:
 
 ```
-#![feature(const_generics)]
 fn foo<T, const N: usize>() {}
 ```