Remove unused features in librustdoc

Author: mu001999

src/librustdoc/lib.rs

@@ -6,12 +6,10 @@
 )]
 #![feature(ascii_char)]
 #![feature(ascii_char_variants)]
-#![feature(box_into_inner)]
 #![feature(box_patterns)]
 #![feature(file_buffered)]
 #![feature(formatting_options)]
 #![feature(if_let_guard)]
-#![feature(iter_advance_by)]
 #![feature(iter_intersperse)]
 #![feature(iter_order_by)]
 #![feature(rustc_private)]