Remove heat_stack_owner role

Since https://review.openstack.org/#/c/128509/ heat no longer requires
the "heat_stack_owner" role by default, as we now delegate all roles
via the trust.  So remove the now unnecessary role creation and assignment
from lib/heat.

Change-Id: Ia097ac9a76b3242ed6e62b11ca64c7ac7680b97c
Merge "Remove heat_stack_owner role"