ofagent: Remove broken XenAPI support

ofagent has code for agent-on-DomU support inherited from OVS agent.
However, it's incomplete and broken.  Because ofagent uses a direct
OpenFlow channel instead of ovs-ofctl command to program a switch,
the method to use the special rootwrap can not work.

Closes-Bug: #1368006
Change-Id: I0bb25a296d1f1e65c233ece6deaef6c095d78707
Merge "ofagent: Remove broken XenAPI support"