Remove unnecessary check from notifications.py
Remove unnecessary check from notifications.py

This check is unnecessary. If the class doesn't have callbacks then
it shouldn't have the resource type defined.

Change-Id: I1f4bc07354707ce3081f54e0a1f9cdfb1d655c08

dstanek/keystone,mahak/keystone,dims/keystone,openstack/keystone,cernops/keystone,roopali8/keystone,rajalokan/keystone,ilay09/keystone,openstack/keystone,takeshineshiro/keystone,dstanek/keystone,idjaw/keystone,dstanek/keystone,klmitch/keystone,himanshu-setia/keystone,rajalokan/keystone,dims/keystone,takeshineshiro/keystone,mahak/keystone,roopali8/keystone,cernops/keystone,idjaw/keystone,rajalokan/keystone,jamielennox/keystone,maestro-hybrid-cloud/keystone,jonnary/keystone,ajayaa/keystone,mahak/keystone,openstack/keystone,klmitch/keystone,ilay09/keystone,himanshu-setia/keystone,maestro-hybrid-cloud/keystone,jamielennox/keystone,jonnary/keystone,ilay09/keystone,ajayaa/keystone