Drop old neutron-grenade job
Drop old neutron-grenade job

This job is still running python 2.7. As we are dropping py2 support in
Ussuri cycle, lets drop this job now.
There is same job called "grenade-py3" which runs on python 3 already
and this is still used in project's CI.

Change-Id: Ie0faac1119c6d2bfea221ba60e26e67b6205909e

mahak/keystone,openstack/keystone,mahak/keystone,mahak/keystone,openstack/keystone,openstack/keystone