Remove handling legacy monasca-agent service file
Remove handling legacy monasca-agent service file

monasca-agent service file is not used anymore. monasca-collector,
monasca-forwarder and monasca-statsd are new services defined in
monasca-agent target.

This change removes the legacy monasca-agent service file handling from
DevStack plugin.

Story: 2000975
Task: 36886

Change-Id: Iac7d608a202440381f211d04b0978218ac36c54d

stackforge/monasca-api,openstack/monasca-api,stackforge/monasca-api,stackforge/monasca-api,openstack/monasca-api,stackforge/monasca-api,openstack/monasca-api