remove feature attributes as const_{array,slice}_from_ref is stabilized

Author: ultrabear

library/core/src/lib.rs

@@ -114,7 +114,6 @@
 #![feature(const_align_offset)]
 #![feature(const_alloc_layout)]
 #![feature(const_arguments_as_str)]
-#![feature(const_array_from_ref)]
 #![feature(const_array_into_iter_constructors)]
 #![feature(const_bigint_helper_methods)]
 #![feature(const_black_box)]
@@ -148,7 +147,6 @@
 #![feature(const_size_of_val)]
 #![feature(const_size_of_val_raw)]
 #![feature(const_slice_from_raw_parts_mut)]
-#![feature(const_slice_from_ref)]
 #![feature(const_slice_split_at_mut)]
 #![feature(const_str_from_utf8_unchecked_mut)]
 #![feature(const_strict_overflow_ops)]