Remove zuul trigger from pbr job.

Change-Id: I7b627cac5044823e9ececa353ded4396925b5766
Reviewed-on: https://review.openstack.org/33486
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Approved: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins