Port_Groups table has been introduced in OVN 2.10 and we've moved in
master to newer version since. This patch removes all references to code
branching between port_groups and address_sets, and also removes
unneeded Address_Set commands and references.
Change-Id: I592d31db9be76d9be202d79d942e15b1668e3c0e
9cbbd8de53