[libc++] Remove unneeded qualifier.

In D117811 @Quuxplusone pointed out the friend declarations don't need
to be qualified. Removing the qualification should avoid needing to add
a GCC work-around when changing _VSTD to std.

Reviewed By: Quuxplusone, philnik, #libc, ldionne

Differential Revision: https://reviews.llvm.org/D118719

libcxx/include/__format/format_arg.h

@@ -140,13 +140,12 @@ class _LIBCPP_TEMPLATE_VIS _LIBCPP_AVAILABILITY_FORMAT basic_format_arg {
   // shall be well-formed when treated as an unevaluated operand.
 
   template <class _Ctx, class... _Args>
-  _LIBCPP_HIDE_FROM_ABI
-      _LIBCPP_AVAILABILITY_FORMAT friend __format_arg_store<_Ctx, _Args...>
-      _VSTD::make_format_args(const _Args&...);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT friend __format_arg_store<_Ctx, _Args...>
+  make_format_args(const _Args&...);
 
   template <class _Visitor, class _Ctx>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_AVAILABILITY_FORMAT friend decltype(auto)
-  _VSTD::visit_format_arg(_Visitor&& __vis, basic_format_arg<_Ctx> __arg);
+  visit_format_arg(_Visitor&& __vis, basic_format_arg<_Ctx> __arg);
 
   union {
     bool __boolean;

libcxx/include/__format/format_context.h

@@ -132,9 +132,8 @@ class
 
   template <class __OutIt, class __CharT>
   friend _LIBCPP_HIDE_FROM_ABI basic_format_context<__OutIt, __CharT>
-  _VSTD::__format_context_create(
-      __OutIt, basic_format_args<basic_format_context<__OutIt, __CharT>>,
-      optional<_VSTD::locale>&&);
+  __format_context_create(__OutIt, basic_format_args<basic_format_context<__OutIt, __CharT>>,
+                          optional<_VSTD::locale>&&);
 
   // Note: the Standard doesn't specify the required constructors.
   _LIBCPP_HIDE_FROM_ABI
@@ -146,8 +145,7 @@ class
 #else
   template <class __OutIt, class __CharT>
   friend _LIBCPP_HIDE_FROM_ABI basic_format_context<__OutIt, __CharT>
-      _VSTD::__format_context_create(
-          __OutIt, basic_format_args<basic_format_context<__OutIt, __CharT>>);
+      __format_context_create(__OutIt, basic_format_args<basic_format_context<__OutIt, __CharT>>);
 
   _LIBCPP_HIDE_FROM_ABI
   explicit basic_format_context(_OutIt __out_it,