[docs] Minor wording changes to drain_filter docs

The docs currently say, "If the closure returns false, it will try
again, and call the closure on the next element."  But this happens
regardless of whether the closure returns true or false.

src/liballoc/linked_list.rs

@@ -747,8 +747,8 @@ impl<T> LinkedList<T> {
     /// Creates an iterator which uses a closure to determine if an element should be removed.
     ///
     /// If the closure returns true, then the element is removed and yielded.
-    /// If the closure returns false, it will try again, and call the closure on the next element,
-    /// seeing if it passes the test.
+    /// If the closure returns false, the element will remain in the list and will not be yielded
+    /// by the iterator.
     ///
     /// Note that `drain_filter` lets you mutate every element in the filter closure, regardless of
     /// whether you choose to keep or remove it.

src/liballoc/vec.rs

@@ -1966,8 +1966,8 @@ impl<T> Vec<T> {
     /// Creates an iterator which uses a closure to determine if an element should be removed.
     ///
     /// If the closure returns true, then the element is removed and yielded.
-    /// If the closure returns false, it will try again, and call the closure
-    /// on the next element, seeing if it passes the test.
+    /// If the closure returns false, the element will remain in the vector and will not be yielded
+    /// by the iterator.
     ///
     /// Using this method is equivalent to the following code:
     ///