Docs(lib/coll/hm): Add kv pair to extract_if's first sentence

Make it consistent in this regard with `BTreeMap`'s.

Signed-off-by: Paul Mabileau <paul.mabileau@harfanglab.fr>

Author: PaulDance

library/std/src/collections/hash/map.rs

@@ -648,7 +648,7 @@ impl<K, V, S> HashMap<K, V, S> {
         Drain { base: self.base.drain() }
     }
 
-    /// Creates an iterator which uses a closure to determine if an element should be removed.
+    /// Creates an iterator which uses a closure to determine if an element (key-value pair) should be removed.
     ///
     /// If the closure returns `true`, the element is removed from the map and
     /// yielded. If the closure returns `false`, or panics, the element remains