Revert "[libc++] ADL-proof <vector> by adding _VSTD:: qualification on calls."

This reverts commit 40267cc989e6d055d5e470681dc7bcfffc72c32f.

Build fails, e.g. http://lab.llvm.org:8011/#/builders/23/builds/108

GitOrigin-RevId: 620adacf87a376ec536ccc66af59df5bb4dc3b38
diff --git a/include/__tree b/include/__tree
index 404351b..4e131a1 100644
--- a/include/__tree
+++ b/include/__tree
@@ -1819,7 +1819,7 @@
     using _VSTD::swap;
     swap(__begin_node_, __t.__begin_node_);
     swap(__pair1_.first(), __t.__pair1_.first());
-    _VSTD::__swap_allocator(__node_alloc(), __t.__node_alloc());
+    __swap_allocator(__node_alloc(), __t.__node_alloc());
     __pair3_.swap(__t.__pair3_);
     if (size() == 0)
         __begin_node() = __end_node();