fix duplicated feature gate

Dylan-DPC · Dylan-DPC · commit db34e352a798 · 2020-08-14T01:05:43.000+02:00
diff --git a/library/alloc/src/lib.rs b/library/alloc/src/lib.rs
@@ -132,7 +132,6 @@
 #![feature(alloc_layout_extra)]
 #![feature(try_trait)]
 #![feature(associated_type_bounds)]
-#![feature(raw_ref_op)]
 // Allow testing this library
 
 #[cfg(test)]
