[clang-tools-extra] [clang-tidy][NFC] Use universal containers mock (PR #186669)

[via cfe-commits]

================
@@ -1,12 +1,8 @@
-// RUN: %check_clang_tidy -std=c++11-or-later %s bugprone-unsafe-functions %t --
+// RUN: %check_clang_tidy -std=c++11-or-later %s bugprone-unsafe-functions %t
 
-namespace std {
-template <class T1, class T2>
-struct pair {
-  T1 first;
-  T2 second;
-};
+#include <utility>
 
+namespace std {
 using ptrdiff_t = long long;
----------------
EugeneZelenko wrote:

Shouldn't it be in `cstddef` mock?

https://github.com/llvm/llvm-project/pull/186669