Clean up the std library's #![feature]s

Signed-off-by: JmPotato <ghzpotato@gmail.com>

library/std/src/lib.rs

@@ -212,7 +212,6 @@
 #![needs_panic_runtime]
 // std may use features in a platform-specific way
 #![allow(unused_features)]
-#![feature(rustc_allow_const_fn_unstable)]
 #![cfg_attr(test, feature(internal_output_capture, print_internals, update_panic_count))]
 #![cfg_attr(
     all(target_vendor = "fortanix", target_env = "sgx"),
@@ -222,22 +221,17 @@
 // std is implemented with unstable features, many of which are internal
 // compiler details that will never be stable
 // NB: the following list is sorted to minimize merge conflicts.
-#![feature(absolute_path)]
 #![feature(alloc_error_handler)]
 #![feature(alloc_layout_extra)]
 #![feature(allocator_api)]
 #![feature(allocator_internals)]
 #![feature(allow_internal_unsafe)]
 #![feature(allow_internal_unstable)]
-#![feature(arbitrary_self_types)]
 #![feature(array_error_internals)]
 #![feature(assert_matches)]
 #![feature(associated_type_bounds)]
 #![feature(async_iterator)]
-#![feature(atomic_mut_ptr)]
-#![feature(auto_traits)]
 #![feature(bench_black_box)]
-#![feature(bool_to_option)]
 #![feature(box_syntax)]
 #![feature(c_unwind)]
 #![feature(c_variadic)]
@@ -248,7 +242,6 @@
 #![feature(char_internals)]
 #![feature(concat_bytes)]
 #![feature(concat_idents)]
-#![feature(const_fn_floating_point_arithmetic)]
 #![feature(const_fn_fn_ptr_basics)]
 #![feature(const_fn_trait_bound)]
 #![feature(const_format_args)]
@@ -257,10 +250,8 @@
 #![feature(const_ipv4)]
 #![feature(const_ipv6)]
 #![feature(const_option)]
-#![feature(const_mut_refs)]
 #![feature(const_socketaddr)]
 #![feature(const_trait_impl)]
-#![feature(container_error_extra)]
 #![feature(c_size_t)]
 #![feature(core_ffi_c)]
 #![feature(core_intrinsics)]
@@ -279,24 +270,17 @@
 #![feature(exact_size_is_empty)]
 #![feature(exhaustive_patterns)]
 #![feature(extend_one)]
-#![feature(fn_traits)]
 #![feature(float_minimum_maximum)]
 #![feature(format_args_nl)]
-#![feature(gen_future)]
-#![feature(generator_trait)]
 #![feature(get_mut_unchecked)]
 #![feature(hashmap_internals)]
 #![feature(int_error_internals)]
-#![feature(integer_atomics)]
-#![feature(int_log)]
-#![feature(into_future)]
 #![feature(intra_doc_pointers)]
 #![feature(lang_items)]
 #![feature(linkage)]
 #![feature(log_syntax)]
 #![feature(map_try_insert)]
 #![feature(maybe_uninit_slice)]
-#![feature(maybe_uninit_uninit_array)]
 #![feature(maybe_uninit_write_slice)]
 #![feature(min_specialization)]
 #![feature(mixed_integer_ops)]
@@ -316,19 +300,14 @@
 #![feature(portable_simd)]
 #![feature(prelude_import)]
 #![feature(ptr_as_uninit)]
-#![feature(ptr_internals)]
 #![feature(raw_os_nonzero)]
 #![feature(rustc_attrs)]
-#![feature(rustc_private)]
 #![feature(saturating_int_impl)]
-#![feature(slice_concat_ext)]
 #![feature(slice_internals)]
 #![feature(slice_ptr_get)]
-#![feature(slice_ptr_len)]
 #![feature(staged_api)]
 #![feature(std_internals)]
 #![feature(stdsimd)]
-#![feature(stmt_expr_attributes)]
 #![feature(str_internals)]
 #![feature(test)]
 #![feature(thread_local)]
@@ -338,8 +317,6 @@
 #![feature(trace_macros)]
 #![feature(try_blocks)]
 #![feature(try_reserve_kind)]
-#![feature(unboxed_closures)]
-#![feature(unwrap_infallible)]
 #![feature(vec_into_raw_parts)]
 // NB: the above list is sorted to minimize merge conflicts.
 #![default_lib_allocator]