remove feature attributes as const_maybe_uninit_as_mut_ptr is stabilized

Author: ultrabear

Diff for: library/alloc/src/lib.rs

@@ -110,7 +110,6 @@
 #![feature(const_cow_is_borrowed)]
 #![feature(const_eval_select)]
 #![feature(const_heap)]
-#![feature(const_maybe_uninit_as_mut_ptr)]
 #![feature(const_maybe_uninit_write)]
 #![feature(const_option)]
 #![feature(const_pin)]

Diff for: library/core/src/lib.rs

@@ -131,7 +131,6 @@
 #![feature(const_ipv4)]
 #![feature(const_ipv6)]
 #![feature(const_likely)]
-#![feature(const_maybe_uninit_as_mut_ptr)]
 #![feature(const_maybe_uninit_assume_init)]
 #![feature(const_nonnull_new)]
 #![feature(const_num_midpoint)]

Diff for: library/core/tests/lib.rs

@@ -26,7 +26,6 @@
 #![feature(const_ipv4)]
 #![feature(const_ipv6)]
 #![feature(const_likely)]
-#![feature(const_maybe_uninit_as_mut_ptr)]
 #![feature(const_nonnull_new)]
 #![feature(const_option)]
 #![feature(const_option_ext)]