[libc++][C++03] remove unused macro in __config (#156609)

The only place this macro was used was in `__memory/aligned_alloc.h`,
but the code that used this macro also checked for C++17 so it was
removed, now this macro is never used.

Author: Un1q32

libcxx/include/__cxx03/__config

@@ -622,18 +622,6 @@ typedef __char32_t char32_t;
 #    define _LIBCPP_HAS_NO_ALIGNED_ALLOCATION
 #  endif
 
-// It is not yet possible to use aligned_alloc() on all Apple platforms since
-// 10.15 was the first version to ship an implementation of aligned_alloc().
-#  if defined(__APPLE__)
-#    if (defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) &&                                                     \
-         __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 101500)
-#      define _LIBCPP_HAS_NO_C11_ALIGNED_ALLOC
-#    endif
-#  elif defined(__ANDROID__) && __ANDROID_API__ < 28
-// Android only provides aligned_alloc when targeting API 28 or higher.
-#    define _LIBCPP_HAS_NO_C11_ALIGNED_ALLOC
-#  endif
-
 #  if defined(__APPLE__) || defined(__FreeBSD__)
 #    define _LIBCPP_HAS_DEFAULTRUNELOCALE
 #  endif