vif: Remove 'plug_vhostuser', 'unplug_vhostuser'

These will never be reached since the '_nova_to_osvif_vif_vhostuser'
function in the 'nova.network.os_vif_util' provides as fallthrough case
since change Ifab3006454708ab290b93f02d82b794c334c3946.

Change-Id: I14ab55178692ff13df114a4c628430561df1a55e
Signed-off-by: Stephen Finucane <sfinucan@redhat.com>

nova/virt/libvirt/vif.py

@@ -694,9 +694,6 @@ class LibvirtGenericVIFDriver(object):
         mtu = network.get_meta('mtu') if network else None
         nova.privsep.linux_net.set_device_mtu(dev, mtu)
 
-    def plug_vhostuser(self, instance, vif):
-        pass
-
     def _plug_os_vif(self, instance, vif):
         instance_info = os_vif_util.nova_to_osvif_instance(instance)
 
@@ -813,9 +810,6 @@ class LibvirtGenericVIFDriver(object):
         except processutils.ProcessExecutionError:
             LOG.exception(_("Failed while unplugging vif"), instance=instance)
 
-    def unplug_vhostuser(self, instance, vif):
-        pass
-
     def _unplug_os_vif(self, instance, vif):
         instance_info = os_vif_util.nova_to_osvif_instance(instance)