rustc_allow_const_fn_unstable is not used in proc_macro

Author: RalfJung

proc_macro/src/lib.rs

@@ -22,7 +22,6 @@
 // This library is copied into rust-analyzer to allow loading rustc compiled proc macros.
 // Please avoid unstable features where possible to minimize the amount of changes necessary
 // to make it compile with rust-analyzer on stable.
-#![feature(rustc_allow_const_fn_unstable)]
 #![feature(staged_api)]
 #![feature(allow_internal_unstable)]
 #![feature(decl_macro)]