Remove leftovers of get_external_network_id for router

Some time ago in patch [1] deprecated option
'gateway_external_network_id' was removed.
After that commit [2] removed rpc function "get_external_network_id"
but there still left some leftovers from this.
This patch removes them completly.

[1] https://review.opendev.org/#/c/666409/
[2] https://review.opendev.org/#/c/682418/

Depends-On: https://review.opendev.org/710429

Change-Id: Ie58ea7f021db051b68be80a1d98f5985ff19fe23

neutron/api/rpc/handlers/l3_rpc.py

@@ -250,18 +250,6 @@ class L3RpcCallback(object):
                 {'port': {portbindings.HOST_ID: host,
                           'device_id': router_id}})
 
-    def get_external_network_id(self, context, **kwargs):
-        """Get one external network id for l3 agent.
-
-        l3 agent expects only one external network when it performs
-        this query.
-        """
-        context = neutron_context.get_admin_context()
-        net_id = self.plugin.get_external_network_id(context)
-        LOG.debug("External network ID returned to l3 agent: %s",
-                  net_id)
-        return net_id
-
     def get_service_plugin_list(self, context, **kwargs):
         return directory.get_plugins().keys()
 

neutron/db/external_net_db.py

@@ -143,13 +143,6 @@ class External_net_db_mixin(object):
         if l3plugin:
             l3plugin.delete_disassociated_floatingips(context, network_id)
 
-    def get_external_network_id(self, context):
-        nets = self.get_networks(context, {extnet_apidef.EXTERNAL: [True]})
-        if len(nets) > 1:
-            raise n_exc.TooManyExternalNetworks()
-        else:
-            return nets[0]['id'] if nets else None
-
     @registry.receives(resources.RBAC_POLICY, [events.BEFORE_CREATE])
     def _process_ext_policy_create(self, resource, event, trigger,
                                    payload=None):