sd-dhcp-server: do not forget previously assigned addresses on pool change

Currently, networkd does not change pool size dynamically, so this
should not change behavior. But if networkd does that, then forgetting
leases causes that an address still used by a client may be assigned to
another host.

src/libsystemd-network/sd-dhcp-server.c

@@ -87,13 +87,6 @@ int sd_dhcp_server_configure_pool(
                 server->address = address->s_addr;
                 server->netmask = netmask;
                 server->subnet = address->s_addr & netmask;
-
-                /* Drop any leases associated with the old address range */
-                hashmap_clear(server->bound_leases_by_address);
-                hashmap_clear(server->bound_leases_by_client_id);
-
-                if (server->callback)
-                        server->callback(server, SD_DHCP_SERVER_EVENT_LEASE_CHANGED, server->callback_userdata);
         }
 
         return 0;