MODE-2303 Removed the "queryableBranches" feature of the Git Connector.

Considering this was in 4.0, removing this will be backward incompatible from a configuration perspective. How about we keep this attribute but with no default, and then in `initialize` we print out a warning if the attribute has a non-null value? That way a repository won't fail starting a 4.0 configuration file that uses this value.

Also need to update the [documentation](https://docs.jboss.org/author/display/MODE40/Git+connector).