Remove unused feature gates

compiler/rustc_query_system/src/lib.rs

@@ -1,12 +1,8 @@
 #![feature(bool_to_option)]
-#![feature(const_panic)]
 #![feature(core_intrinsics)]
-#![feature(drain_filter)]
 #![feature(hash_raw_entry)]
 #![feature(iter_zip)]
 #![feature(min_specialization)]
-#![feature(stmt_expr_attributes)]
-#![feature(trusted_step)]
 
 #[macro_use]
 extern crate tracing;