Remove release_lease from the DHCP driver interface
Remove release_lease from the DHCP driver interface

Neither the midonet nor the linux dhcp driver needs a call to
release_lease.  Removing this from the driver API simplifies more code
in the DHCP agent.

Change-Id: Ib144b2bf3720b1b999205ace1a7d1ffe5ef3b167
Closes-Bug: #1269505

JoeMido/networking-midonet,yamt/networking-midonet,midokura/python-neutron-plugin-midonet,midokura/python-neutron-plugin-midonet,midonet/python-neutron-plugin-midonet,midonet/python-neutron-plugin-midonet,yamt/networking-midonet,JoeMido/networking-midonet