Remove cons_mouse_setting() stub

Mouse support has been disabled long ago.

tests/unittests/ui/stub_ui.c

@@ -429,7 +429,6 @@ void cons_wrap_setting(void) {}
 void cons_winstidy_setting(void) {}
 void cons_encwarn_setting(void) {}
 void cons_time_setting(void) {}
-void cons_mouse_setting(void) {}
 void cons_statuses_setting(void) {}
 void cons_wintitle_setting(void) {}
 void cons_notify_setting(void) {}