wxPython4 sequels: fix exception in connection dialog, force black text in FBD.

- wxPython4 does not have RemoveSizer in API anymore.
- On GTK3 with dark theme default text colour is white, making it unreadable.

#!/bin/bash

CONTAINER=beremiz_sikuli_current

docker start $CONTAINER
docker exec -i -t -u root $CONTAINER bash
docker stop $CONTAINER