Remove the "queryable" feature of the Git Connector

With the new query engine & indexing changes in 4.x, querying any part of a Git connector becomes problematic, because it means that even with indexes in place, depending on the contents of the query we'd have too crawl entire Git branches, which takes forever.

This was hinted towards in MODE-1741, but for 3.x this made more sense. So in 4.x we should remove the queryable feature of the connector altogether.