lib/tempest: Liberty EOL: remove the volume_services feature flag
lib/tempest: Liberty EOL: remove the volume_services feature flag

Now that Liberty is EOLed, the feature flag is not needed anymore.

Change-Id: Ib82cb21edbda383d17f8cf69fedc884f2357fead
Depends-On: I7073106988a79aad19c6b95bb050d2eaf00c36c0

noironetworks/devstack,dtroyer/devstack,openstack-dev/devstack,richliu/devstack,group-policy/devstack,dtroyer/devstack,noironetworks/devstack,nawawi/openstack,group-policy/devstack,nawawi/openstack,richliu/devstack,openstack-dev/devstack