Remove old releases specific code
Remove old releases specific code

Liberty and Mitaka releases are EOL.
For better readability, we remove this chunk of code.

Change-Id: I8cdbed77bd191cae8385b42cf4785ce978c4c4ca

openstack-packages/DLRN,openstack-packages/DLRN,openstack-packages/delorean,openstack-packages/delorean