core: Remove GetVdsByHostQuery leftovers

Removed the VdcQueryType.GetVdsByHost constant and the
GetVdsByHostParameters class as the GetVdsByHost query no longer
exists in the codebase.

Change-Id: Ib426d8ae35d8536286f02dc67141b0f641f43971
Signed-off-by: Allon Mureinik <amureini@redhat.com>