Clean old lsif redis-store data on startup.

Created by: efritz

Attempt to remove all bull:* keys from redis-store on LSIF server startup. This code will exist for two minor releases (along with some other migration paths that run on startup until 3.15). This will temporarily add the communication link between lsif-server and redis-store, but should not require any doc changes as this is a best-effort cleanup of stale data on customer instances.