Although Deployment already applied its ControllerRef to adopt matching
ReplicaSets, it actually still used label selectors to list objects that
it controls. That meant it didn't actually follow the rules of
ControllerRef, so it could still fight with other controller types.

This should mean that the special handling for overlapping Deployments
is no longer necessary, since each Deployment will only see objects that
it owns (via ControllerRef).