[libcxx] [test] Remove an incorrect TEST_HAS_ALIGNED_ALLOC define from test_macros.h

This was added inconsistently in
19fd9039; Windows doesn't have the
aligned_alloc function (neither MSVC nor MinGW toolchains) and we don't
define _LIBCPP_HAS_ALIGNED_ALLOC while building libcxx.

Differential Revision: https://reviews.llvm.org/D103399