[hotfix] fix port configs for signald-2
- BUG: p8s fails to scrape metrics from signald-2
- CAUSE: the signald-2 container exposed port 5003 instead of port 5002
- FIX: expose the right port
while at it: remove extraneous VIRTUAL_PORT
env vars from base
docker-compose
file (since we provide this in prod compose file and
they are only meaningful there)