Stabilize binary_heap_retain

FCP finished in tracking issue: rust-lang#71503

Author: Amanieu

library/alloc/src/collections/binary_heap/mod.rs

@@ -837,7 +837,6 @@ impl<T: Ord> BinaryHeap<T> {
     /// Basic usage:
     ///
     /// ```
-    /// #![feature(binary_heap_retain)]
     /// use std::collections::BinaryHeap;
     ///
     /// let mut heap = BinaryHeap::from([-10, -5, 1, 2, 4, 13]);
@@ -846,7 +845,7 @@ impl<T: Ord> BinaryHeap<T> {
     ///
     /// assert_eq!(heap.into_sorted_vec(), [-10, 2, 4])
     /// ```
-    #[unstable(feature = "binary_heap_retain", issue = "71503")]
+    #[stable(feature = "binary_heap_retain", since = "CURRENT_RUSTC_VERSION")]
     pub fn retain<F>(&mut self, mut f: F)
     where
         F: FnMut(&T) -> bool,

library/alloc/tests/lib.rs

@@ -25,7 +25,6 @@
 #![feature(binary_heap_into_iter_sorted)]
 #![feature(binary_heap_drain_sorted)]
 #![feature(slice_ptr_get)]
-#![feature(binary_heap_retain)]
 #![feature(binary_heap_as_slice)]
 #![feature(inplace_iteration)]
 #![feature(iter_advance_by)]