Remove filter from all searches when deleting an issue

This query shows that we have alerts or saved searches or widgets that have `issue: FOO` in their syntax and they're raising errors in our systems.

I assume it happens because an issue has been deleted but the filter still exists in various places.

For instance, if you [query for issue SENTRY-14ZS](https://sentry.sentry.io/discover/results/?field=title&field=release&field=environment&field=user.display&field=timestamp&name=VisitationError%3A+SoftTimeLimitExceeded%3A+SoftTimeLimitExceeded%28%29&project=1&query=issue%3ASENTRY-14ZS&sort=-timestamp&statsPeriod=90d&yAxis=count%28%29) (which is alerting) you will that issue does not exist anymore [1].

I assume this work will entail hooking up to the deletion code to remove the issue and remove it from all queries.

[1]