Remove the TripleO standalone job
Remove the TripleO standalone job

Despite the comment in .zuul.yaml this job actually doesn't use Mistral.
It is installed, but not used. This can be seen in the Mistral logs
which have minimal output (other than that of the workbooks being
loaded).

https://c867b5a19c86ae8c3ab7-a51f273e08e05c861a2fa6ace8476176.ssl.cf1.rackcdn.com/695212/2/check/tripleo-ci-centos-7-scenario003-standalone/4827980/logs/undercloud/var/log/containers/mistral/

Th other TripleO job also covers this case and then uses Mistral. This
patch removes the job which has been wasting resources for quite some
time now.

Change-Id: Ie3381c7226d50591192ae61697bdb0d134ddf4f1

openstack/mistral,openstack/mistral