<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _router_removed(self, router_id, deconfigure=True):
 """Operations when a router is removed. Get the RouterInfo object corresponding to the router in the service helpers's router_info dict. If deconfigure is set to True, remove this router's configuration from the hosting device. :param router_id: id of the router :param deconfigure: if True, the router's configuration is deleted from the hosting device. :return: None """

        ri = self.router_info.get(router_id)
        if ri is None:
            LOG.warning("Info for router %s was not found. "
                        "Skipping router removal.", router_id)
            return
        ri.router['gw_port'] = None
        ri.router[bc.constants.INTERFACE_KEY] = []
        ri.router[bc.constants.FLOATINGIP_KEY] = []
        try:
            hd = ri.router['hosting_device']
            # We proceed to removing the configuration from the device
            # only if (a) deconfigure is set to True (default)
            # (b) the router's hosting device is reachable.
            if (deconfigure and
                    self._dev_status.is_hosting_device_reachable(hd)):
                self._process_router(ri)
                driver = self.driver_manager.get_driver(router_id)
                driver.router_removed(ri)
                self.driver_manager.remove_driver(router_id)
            del self.router_info[router_id]
            self._del_from_removed_routers_cache(router_id)
        except cfg_exceptions.DriverException:
            LOG.warning("Router remove for router_id: %s was incomplete. "
                        "Adding the router to removed_routers list",
                        router_id)
            self._update_removed_routers_cache([router_id])
            # remove this router from updated_routers if it is there. It might
            # end up there too if exception was thrown earlier inside
            # `_process_router()`
            self._del_from_updated_routers_cache(router_id)
        except ncc_errors.SessionCloseError as e:
            LOG.exception("ncclient Unexpected session close %s"
                          " while attempting to remove router", e)
            if not self._dev_status.is_hosting_device_reachable(hd):
                LOG.debug("Lost connectivity to Hosting Device %s" % hd['id'])
                # rely on heartbeat to detect HD state
                # and schedule resync when the device comes back
            else:
                # retry the router removal on the next pass
                self._update_removed_routers_cache([router_id])
                LOG.debug("Interim connectivity lost to hosting device %s, "
                          "enqueuing router %s in removed_routers set" %
                          pp.pformat(hd), router_id)