Revert "[libc++] Correctly handle Objective-C++ ARC qualifiers in std::is_pointer"

This broke the Chromium build on Mac, see https://crbug.com/949071

> Summary:
> Otherwise, std::is_pointer<id __strong> works, but std::is_pointer<id __weak>
> (and others) don't work as expected.
>
> rdar://problem/49126333
>
> Reviewers: ahatanak, EricWF
>
> Subscribers: christof, jkorous, dexonsmith, libcxx-commits
>
> Differential Revision: https://reviews.llvm.org/D60087

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@357569 91177308-0d34-0410-b5e6-96231b3b80d8

include/type_traits

@@ -784,11 +784,6 @@ _LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_array_v
 
 template <class _Tp> struct __libcpp_is_pointer       : public false_type {};
 template <class _Tp> struct __libcpp_is_pointer<_Tp*> : public true_type {};
-#if defined(_LIBCPP_HAS_OBJC_ARC)
-template <class _Tp> struct __libcpp_is_pointer<_Tp* __weak> : public true_type {};
-template <class _Tp> struct __libcpp_is_pointer<_Tp* __autoreleasing> : public true_type {};
-template <class _Tp> struct __libcpp_is_pointer<_Tp* __unsafe_unretained> : public true_type {};
-#endif
 
 template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_pointer
     : public __libcpp_is_pointer<typename remove_cv<_Tp>::type> {};

test/libcxx/type_traits/is_pointer_objc.arc.pass.mm

@@ -1,56 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-//
-// UNSUPPORTED: c++98, c++03
-
-// <type_traits>
-
-// std::is_pointer
-
-// Test that we correctly handle Objective-C++ ARC qualifiers on pointers.
-
-#include <type_traits>
-
-
-template <typename T>
-void test() {
-    static_assert(std::is_pointer<T __weak>::value, "");
-    static_assert(std::is_pointer<T __strong>::value, "");
-    static_assert(std::is_pointer<T __autoreleasing>::value, "");
-    static_assert(std::is_pointer<T __unsafe_unretained>::value, "");
-
-    static_assert(std::is_pointer<T __weak const>::value, "");
-    static_assert(std::is_pointer<T __strong const>::value, "");
-    static_assert(std::is_pointer<T __autoreleasing const>::value, "");
-    static_assert(std::is_pointer<T __unsafe_unretained const>::value, "");
-
-    static_assert(std::is_pointer<T __weak volatile>::value, "");
-    static_assert(std::is_pointer<T __strong volatile>::value, "");
-    static_assert(std::is_pointer<T __autoreleasing volatile>::value, "");
-    static_assert(std::is_pointer<T __unsafe_unretained volatile>::value, "");
-
-    static_assert(std::is_pointer<T __weak const volatile>::value, "");
-    static_assert(std::is_pointer<T __strong const volatile>::value, "");
-    static_assert(std::is_pointer<T __autoreleasing const volatile>::value, "");
-    static_assert(std::is_pointer<T __unsafe_unretained const volatile>::value, "");
-}
-
-@class Foo;
-
-int main(int, char**) {
-    test<id>();
-    test<id const>();
-    test<id volatile>();
-    test<id const volatile>();
-    test<Foo*>();
-    test<Foo const*>();
-    test<Foo volatile*>();
-    test<Foo const volatile*>();
-
-    return 0;
-}