Remove impossible _MSC_VER check

Summary:
It is immediately preceded by this check:
  #if _MSC_VER < 1900
  #error "MSVC versions prior to Visual Studio 2015 are not supported"
  #endif

Reviewers: EricWF

Subscribers: christof, cfe-commits

Differential Revision: https://reviews.llvm.org/D45829

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@330360 91177308-0d34-0410-b5e6-96231b3b80d8

include/__config

@@ -586,9 +586,6 @@ namespace std {
 #define _LIBCPP_HAS_NO_CONSTEXPR
 #define _LIBCPP_HAS_NO_CXX14_CONSTEXPR
 #define _LIBCPP_HAS_NO_VARIABLE_TEMPLATES
-#if _MSC_VER <= 1800
-#define _LIBCPP_HAS_NO_UNICODE_CHARS
-#endif
 #define _LIBCPP_HAS_NO_NOEXCEPT
 #define __alignof__ __alignof
 #define _LIBCPP_NORETURN __declspec(noreturn)