Desupport neutron openvswitch and linuxbridge monolithic plugins

These plugins were removed in Juno.
Note: this doesn't affect the corresponding ML2 mechanism drivers.

Partial-Bug: #1323729
Change-Id: Ia8da1e20a03fef5657ba1584bf83ddd224b5d5f2
diff --git a/lib/neutron_plugins/openvswitch b/lib/neutron_plugins/openvswitch
index c468132..e9bc5f9 100644
--- a/lib/neutron_plugins/openvswitch
+++ b/lib/neutron_plugins/openvswitch
@@ -1,5 +1,8 @@
-# Neutron Open vSwitch plugin
-# ---------------------------
+# Common code used by cisco and embrane plugins
+# ---------------------------------------------
+
+# This module used to be for Open vSwitch monolithic plugin,
+# which has been removed in Juno.
 
 # Save trace setting
 OVS_XTRACE=$(set +o | grep xtrace)