move: drop has_mbyte check

has_mbyte is always true in nvim.

src/nvim/move.c

@@ -2168,9 +2168,7 @@ void do_check_cursorbind(void)
         restart_edit = restart_edit_save;
       }
       // Correct cursor for multi-byte character.
-      if (has_mbyte) {
-        mb_adjust_cursor();
-      }
+      mb_adjust_cursor();
       redraw_later(VALID);
 
       // Only scroll when 'scrollbind' hasn't done this.