refactor(messages): fold msg_attr into msg

problem: there are too many different functions in message.c
solution: fold some of the functions into themselves

src/nvim/ex_getln.c

@@ -2664,7 +2664,7 @@ static void abandon_cmdline(void)
   if (msg_scrolled == 0) {
     compute_cmdrow();
   }
-  msg("");
+  msg("", 0);
   redraw_cmdline = true;
 }