remove external_network_bridge option

The external_network_bridge option is deprecated/legacy and being
removed from neutron (see I07474713206c218710544ad98c08caaa37dbf53a).
This patch removes the external_network_bridge option iniset from
devstack scripts.

Change-Id: I4d9641cc9bb83719c9af1edabb89a63c4c2b1d96

Author: Hongbin Lu

lib/neutron

@@ -95,9 +95,6 @@ NEUTRON_ROOTWRAP_CONF_FILE=$NEUTRON_CONF_DIR/rootwrap.conf
 NEUTRON_ROOTWRAP_CMD="$NEUTRON_ROOTWRAP $NEUTRON_ROOTWRAP_CONF_FILE"
 NEUTRON_ROOTWRAP_DAEMON_CMD="$NEUTRON_ROOTWRAP-daemon $NEUTRON_ROOTWRAP_CONF_FILE"
 
-# This is needed because _neutron_ovs_base_configure_l3_agent will set
-# external_network_bridge
-Q_USE_PROVIDERNET_FOR_PUBLIC=${Q_USE_PROVIDERNET_FOR_PUBLIC:-True}
 # This is needed because _neutron_ovs_base_configure_l3_agent uses it to create
 # an external network bridge
 PUBLIC_BRIDGE=${PUBLIC_BRIDGE:-br-ex}

lib/neutron_plugins/ovs_base

@@ -96,10 +96,6 @@ function _neutron_ovs_base_configure_firewall_driver {
 }
 
 function _neutron_ovs_base_configure_l3_agent {
-    if [ "$Q_USE_PROVIDERNET_FOR_PUBLIC" != "True" ]; then
-        iniset $Q_L3_CONF_FILE DEFAULT external_network_bridge $PUBLIC_BRIDGE
-    fi
-
     neutron-ovs-cleanup --config-file $NEUTRON_CONF
     if [[ "$Q_USE_PUBLIC_VETH" = "True" ]]; then
         ip link show $Q_PUBLIC_VETH_INT > /dev/null 2>&1 ||