Revert "report message even if no action is specified"

This reverts commit 031e23f723
and commit 9ba2068664.

This breaks the ability to have silent pipelines.

Instead, how about the following:

  pipelines:
  - name: postmerge
    manager: IndependentPipelineManager
    ...
    success:
      force-message: true

That should work without any additional code.

Change-Id: I0d15b8fcb678a36c46205693ba9a6756ec6a076f
Reviewed-on: https://review.openstack.org/29180
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Antoine Musso <hashar@free.fr>
Approved: James E. Blair <corvus@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins

zuul/trigger/gerrit.py

@@ -131,8 +131,8 @@ class Gerrit(object):
         if not change.number:
             self.log.debug("Change has no number; not reporting")
             return
-        if not action and not message:
-            self.log.debug("No action or message specified; not reporting")
+        if not action:
+            self.log.debug("No action specified; not reporting")
             return
         changeid = '%s,%s' % (change.number, change.patchset)
         ref = 'refs/heads/' + change.branch