[NFC] Remove max_align.c LIT testcase

Since we fixed the definition of `SuitableAlign`[https://reviews.llvm.org/D88659],
`max_align_t` and `__BIGGEST_ALIGNMENT__` are not necessarily the same always.

The original testcase was added here: https://reviews.llvm.org/D59048

Differential Revision: https://reviews.llvm.org/D90187

clang/test/Headers/max_align.c

@@ -1,12 +0,0 @@
-// RUN: %clang_cc1 -fsyntax-only -std=c11 -verify %s
-// expected-no-diagnostics
-
-// XFAIL: windows-, i686
-
-#ifndef __BIGGEST_ALIGNMENT__
-#error __BIGGEST_ALIGNMENT__ not defined
-#endif
-
-#include <stddef.h>
-
-_Static_assert(__BIGGEST_ALIGNMENT__ == _Alignof(max_align_t), "");