Make const_generics_defaults not an incomplete feature

compiler/rustc_feature/src/active.rs

@@ -692,7 +692,6 @@ pub const INCOMPLETE_FEATURES: &[Symbol] = &[
     sym::repr128,
     sym::unsized_locals,
     sym::capture_disjoint_fields,
-    sym::const_generics_defaults,
     sym::inherent_associated_types,
     sym::type_alias_impl_trait,
     sym::native_link_modifiers,

src/test/ui/const-generics/defaults/const-param-as-default-value.rs

@@ -1,6 +1,5 @@
 // run-pass
 #![feature(const_generics_defaults)]
-#![allow(incomplete_features)]
 struct Foo<const N: usize, const M: usize = N>([u8; N], [u8; M]);
 
 fn foo<const N: usize>() -> Foo<N> {

src/test/ui/const-generics/defaults/const-param-in-ty-defaults.rs

@@ -1,6 +1,5 @@
 // run-pass
 #![feature(const_generics_defaults)]
-#![allow(incomplete_features)]
 struct Foo<const N: usize, T = [u8; N]>(T);
 
 impl<const N: usize> Foo<N> {

src/test/ui/const-generics/defaults/default-param-wf-concrete.rs

@@ -1,5 +1,4 @@
 #![feature(const_generics_defaults)]
-#![allow(incomplete_features)]
 struct Foo<const N: u8 = { 255 + 1 }>;
 //~^ ERROR evaluation of constant value failed
 fn main() {}

src/test/ui/const-generics/defaults/default-param-wf-concrete.stderr

@@ -1,5 +1,5 @@
 error[E0080]: evaluation of constant value failed
-  --> $DIR/default-param-wf-concrete.rs:3:28
+  --> $DIR/default-param-wf-concrete.rs:2:28
    |
 LL | struct Foo<const N: u8 = { 255 + 1 }>;
    |                            ^^^^^^^ attempt to compute `u8::MAX + 1_u8`, which would overflow

src/test/ui/const-generics/defaults/pretty-printing-ast.rs

@@ -4,7 +4,6 @@
 
 #![crate_type = "lib"]
 #![feature(const_generics_defaults)]
-#![allow(incomplete_features)]
 
 trait Foo<const KIND: bool = true> {}
 

src/test/ui/const-generics/defaults/pretty-printing-ast.stdout

@@ -6,7 +6,6 @@
 
 #![crate_type = "lib"]
 #![feature(const_generics_defaults)]
-#![allow(incomplete_features)]
 #[prelude_import]
 use ::std::prelude::rust_2015::*;
 #[macro_use]

src/test/ui/const-generics/defaults/repr-c-issue-82792.rs

@@ -3,7 +3,6 @@
 // run-pass
 
 #![feature(const_generics_defaults)]
-#![allow(incomplete_features)]
 
 #[repr(C)]
 pub struct Loaf<T: Sized, const N: usize = 1> {

src/test/ui/const-generics/min_const_generics/default_function_param.rs

@@ -1,6 +1,5 @@
 #![crate_type = "lib"]
 #![feature(const_generics_defaults)]
-#![allow(incomplete_features)]
 
 fn foo<const SIZE: usize = 5usize>() {}
 //~^ ERROR defaults for const parameters are

src/test/ui/const-generics/min_const_generics/default_function_param.stderr

@@ -1,5 +1,5 @@
 error: defaults for const parameters are only allowed in `struct`, `enum`, `type`, or `trait` definitions
-  --> $DIR/default_function_param.rs:5:14
+  --> $DIR/default_function_param.rs:4:14
    |
 LL | fn foo<const SIZE: usize = 5usize>() {}
    |              ^^^^

src/test/ui/derives/derive-macro-const-default.rs

@@ -1,5 +1,4 @@
 // check-pass
-#![allow(incomplete_features)]
 #![feature(const_generics_defaults)]
 
 #[derive(Clone, PartialEq, Debug)]