[NFC] Rename _LIBCPP_TYPE_VIS_ONLY to _LIBCPP_TEMPLATE_VIS

The name _LIBCPP_TYPE_VIS_ONLY is no longer accurate because both
_LIBCPP_TYPE_VIS and _LIBCPP_TYPE_VIS_ONLY expand to
__attribute__((__type_visibility__)) with Clang. The only remaining difference
is that _LIBCPP_TYPE_VIS_ONLY can be applied to templates whereas
_LIBCPP_TYPE_VIS cannot (due to dllimport/dllexport not being allowed on
templates).

This patch renames _LIBCPP_TYPE_VIS_ONLY to _LIBCPP_TEMPLATE_VIS.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@291035 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/streambuf b/include/streambuf
index 6c47838..8607065 100644
--- a/include/streambuf
+++ b/include/streambuf
@@ -119,7 +119,7 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _CharT, class _Traits>
-class _LIBCPP_TYPE_VIS_ONLY basic_streambuf
+class _LIBCPP_TEMPLATE_VIS basic_streambuf
 {
 public:
     // types: