Fix handling of combined sky maps

There has been a sentry error where a combined sky map was chose as the preferred sky map: https://sentry.io/organizations/ligo-caltech/issues/3233200370/?environment=test&project=1425216&query=is%3Aunresolved&statsPeriod=14d

This should not be the default behavior and should instead default to a GW-only sky map, while the RAVEN coincidence section should use the joint sky map instead. This could be done by excluding any sky map with -ext in it.