Verify: remove useless check in _VerifyInstance

Verify: remove useless check in _VerifyInstance

The list of instances passed to _VerifyInstance is the one coming from
self.cfg.GetInstanceList(). So there's no point, inside that function, in
checking whether the current instance is a member of that list. Moreover
orphaned instance verification is already done in a separate step.

Reviewed-by: imsnah