Remove deprecation notice in LibvirtBridgeDriver

After further discussions with Quantum team, it was agreed
not to deprecate the existing libvirt VIF drivers until the
Havana release, to allow more time for Quantum plugins to be
updated.

Blueprint: libvirt-vif-driver
Change-Id: I0226c4117630de489543d35662a8ee6b6c7729f9
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Merge "Remove deprecation notice in LibvirtBridgeDriver"