Remove useless parameter from l3_dvr_db.py

clear_unused_fip_agent_gw_port and check_fips_availability_on_host
functions in l3_dvr_db.py contain a useless parameter fip_id which
can be removed.

Change-Id: Ibc14f9d9cd4b35a5f3b8d1a733d2ef40743e8077
Merge "Remove useless parameter from l3_dvr_db.py"
Merge branch 'master' of https://github.com/openstack/quantum