Remove #![feature(const_generics)] and #![allow(incomplete_features)]

Author: hyd-dev

src/lib.rs

@@ -8,9 +8,6 @@
 #![warn(rust_2018_idioms)]
 #![allow(clippy::cast_lossless)]
 
-#![allow(incomplete_features)]
-#![feature(const_generics)]
-
 extern crate rustc_attr;
 extern crate rustc_apfloat;
 extern crate rustc_ast;