Bug 1076886 - Deploy: Don't specify the wrong revision to New Relic

We're passing settings.UPDATE_REF, which is the default ref value, not
the actual value that was passed via the Chief web UI. As such, New
Relic was always displaying the revision deployed as "master", even if
it was a non-master branch deploy. Ideally we'd use the value of 'ref'
from pre_update(), but that's not available during the deploy() task
(the script is run in three independent stages & Chief unhelpfully only
passes 'ref' to the first stage), so we'll have to read it back from the
media/revision file - which will require more mangling in bug 1076886.

For now, seeing as the 'revision' property is optional, lets just omit
it, rather than setting it to a sometimes wrong value.

deployment/update/update.py

@@ -135,7 +135,6 @@ def ping_newrelic(ctx):
         print 'Post deployment to New Relic'
         data = urllib.urlencode({
             'deployment[user]': 'Chief',
-            'deployment[revision]': settings.UPDATE_REF,
             'deployment[application_id]': settings.NEW_RELIC_APP_ID
         })
         headers = {'x-api-key': settings.NEW_RELIC_API_KEY}