[libc++] Remove unused _LIBCPP_FUNC_VIS_ONLY

This has been unused since r282644.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@307965 91177308-0d34-0410-b5e6-96231b3b80d8

include/__config

@@ -625,7 +625,6 @@ namespace std {
 #define _LIBCPP_HIDDEN
 #define _LIBCPP_METHOD_TEMPLATE_IMPLICIT_INSTANTIATION_VIS
 #define _LIBCPP_TEMPLATE_VIS
-#define _LIBCPP_FUNC_VIS_ONLY
 #define _LIBCPP_ENUM_VIS
 
 #if defined(_LIBCPP_COMPILER_MSVC)
@@ -684,10 +683,6 @@ namespace std {
 #  endif
 #endif
 
-#ifndef _LIBCPP_FUNC_VIS_ONLY
-# define _LIBCPP_FUNC_VIS_ONLY _LIBCPP_FUNC_VIS
-#endif
-
 #ifndef _LIBCPP_EXTERN_VIS
 # define _LIBCPP_EXTERN_VIS
 #endif