Remove unused feature gates

compiler/rustc_target/src/lib.rs

@@ -9,13 +9,11 @@
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![feature(bool_to_option)]
-#![feature(const_panic)]
 #![feature(nll)]
 #![feature(never_type)]
 #![feature(associated_type_bounds)]
 #![feature(exhaustive_patterns)]
 #![feature(min_specialization)]
-#![feature(trusted_step)]
 
 use std::path::{Path, PathBuf};