always return (owned or non-owned, depending on build) wxScopedCharBuffer from utf8_str() and ToUTF8()

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@59945 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/buffer.h

@@ -427,13 +427,6 @@ typedef wxWritableCharTypeBuffer<wchar_t> wxWritableWCharBuffer;
     #define wxWX2WCbuf wxWCharBuffer
 #endif // Unicode/ANSI
 
-// type of the value returned by wxString::utf8_str()
-#if wxUSE_UNICODE_UTF8
-    #define wxUTF8Buf char *
-#else
-    #define wxUTF8Buf wxCharBuffer
-#endif
-
 // ----------------------------------------------------------------------------
 // A class for holding growable data buffers (not necessarily strings)
 // ----------------------------------------------------------------------------