remove constraints arg from pip installation of self in releasenotes jobs
remove constraints arg from pip installation of self in releasenotes jobs

We cannot use constraints when installing the current project because
that makes it impossible to install the source for anything that
appears in the constraints list.

Change-Id: I6a9cdce650e47c9d88d36b11e3a57cc41bc92ca6
Signed-off-by: Doug Hellmann <0798ebecfb7bc4dfb9d0445c2fa030eb64e1fa1c@doughellmann.com>

openstack-infra/openstack-zuul-jobs,openstack-infra/openstack-zuul-jobs