Remove deprecated list_notifier_drivers option
Remove deprecated list_notifier_drivers option

It was deprecated in Juno, and should be deleted in Liberty
regarding doc [1].

[1]: https://etherpad.openstack.org/p/YVR-heat-liberty-deprecation

Change-Id: Ie1b85f88f6851e7c2638471972ac06991955f9d6

dims/heat,rh-s/heat,jasondunsmore/heat,pratikmallya/heat,cwolferh/heat-scratch,dragorosson/heat,cryptickp/heat,takeshineshiro/heat,dims/heat,srznew/heat,miguelgrinberg/heat,dragorosson/heat,srznew/heat,cryptickp/heat,maestro-hybrid-cloud/heat,miguelgrinberg/heat,maestro-hybrid-cloud/heat,gonzolino/heat,openstack/heat,noironetworks/heat,noironetworks/heat,steveb/heat,pratikmallya/heat,cwolferh/heat-scratch,rh-s/heat,takeshineshiro/heat,openstack/heat,gonzolino/heat,steveb/heat,jasondunsmore/heat