libvirt: remove unused Service.get_by_compute_host mocks
libvirt: remove unused Service.get_by_compute_host mocks

Change Iefd7a60139043929aee63a3660fabdded1622029 made these
mocks unnecessary so this change just removes them.

Change-Id: I6fbeef09d868ff7c179f8e791944cc6e8ae10802

klmitch/nova,openstack/nova,mahak/nova,rahulunair/nova,mahak/nova,mahak/nova,rahulunair/nova,openstack/nova,klmitch/nova,klmitch/nova,openstack/nova,rahulunair/nova,klmitch/nova