Rollup merge of rust-lang#70712 - :stabilize-remove-entry, r=Amanieu

stabilize BTreeMap::remove_entry

This PR stabilizes `BTreeMap::remove_entry` as implemented in rust-lang#68378.

Closes rust-lang#66714

Author: Dylan-DPC

src/liballoc/collections/btree/map.rs

@@ -923,15 +923,14 @@ impl<K: Ord, V> BTreeMap<K, V> {
     /// Basic usage:
     ///
     /// ```
-    /// #![feature(btreemap_remove_entry)]
     /// use std::collections::BTreeMap;
     ///
     /// let mut map = BTreeMap::new();
     /// map.insert(1, "a");
     /// assert_eq!(map.remove_entry(&1), Some((1, "a")));
     /// assert_eq!(map.remove_entry(&1), None);
     /// ```
-    #[unstable(feature = "btreemap_remove_entry", issue = "66714")]
+    #[stable(feature = "btreemap_remove_entry", since = "1.44.0")]
     pub fn remove_entry<Q: ?Sized>(&mut self, key: &Q) -> Option<(K, V)>
     where
         K: Borrow<Q>,