Remove redundant #![feature(...)] 's from compiler/

compiler/rustc_mir/src/lib.rs

@@ -13,15 +13,12 @@ Rust MIR: a lowered representation of Rust.
 #![feature(const_panic)]
 #![feature(crate_visibility_modifier)]
 #![feature(decl_macro)]
-#![feature(drain_filter)]
 #![feature(exact_size_is_empty)]
 #![feature(exhaustive_patterns)]
-#![feature(iter_order_by)]
 #![feature(never_type)]
 #![feature(min_specialization)]
 #![feature(trusted_len)]
 #![feature(try_blocks)]
-#![feature(associated_type_bounds)]
 #![feature(associated_type_defaults)]
 #![feature(stmt_expr_attributes)]
 #![feature(trait_alias)]