Remove recipe[openstack-identity::db] from the identity roles

The db recipe was removed in commit 54e05e5f2e6f57934310c10d418ab263a9eb14bf
on stackforge/cookbook-openstack-identity.  Updating the role to reflect
this.

Change-Id: I27740b496e65581bd3d92d7182ad55bc5e0fe108
Merge "Remove recipe[openstack-identity::db] from the identity roles"