Revert "[libc++] Build <filesystem> support as part of the dylib"

When I applied r356500 (https://reviews.llvm.org/D59152), I somehow
deleted all of filesystem's tests. I will revert r356500 and re-apply
it properly.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@356505 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/input.output/filesystems/fs.req.namespace/namespace.fail.cpp

@@ -0,0 +1,30 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: c++98 || c++03 || c++11 || c++14
+
+// <filesystem>
+
+// namespace std::filesystem
+
+#include <filesystem>
+#include "test_macros.h"
+
+using namespace std::filesystem;
+
+#if TEST_STD_VER >= 11
+// expected-error@-3 {{no namespace named 'filesystem' in namespace 'std';}}
+#else
+// expected-error@-5 {{expected namespace name}}
+#endif
+
+int main(int, char**) {
+
+
+  return 0;
+}