Deactivate feature gate explicit_generic_args_with_impl_trait

Signed-off-by: Nick Cameron <nrc@ncameron.org>

compiler/rustc_error_codes/src/error_codes/E0632.md

@@ -1,9 +1,11 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 An explicit generic argument was provided when calling a function that
 uses `impl Trait` in argument position.
 
 Erroneous code example:
 
-```compile_fail,E0632
+```ignore (no longer an error)
 fn foo<T: Copy>(a: T, b: impl Clone) {}
 
 foo::<i32>(0i32, "abc".to_string());