Remove unused features.

Author: nnethercote

compiler/rustc_infer/src/lib.rs

@@ -19,10 +19,7 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![doc(rust_logo)]
 #![feature(assert_matches)]
-#![feature(box_patterns)]
 #![feature(extend_one)]
-#![feature(if_let_guard)]
-#![feature(iter_intersperse)]
 #![feature(iterator_try_collect)]
 #![feature(let_chains)]
 #![feature(rustdoc_internals)]