bridge: Remove unused declaration br_multicast_set_hash_max()

Since commit 19e3a9c9 ("net: bridge: convert multicast to generic rhashtable")
this is not used, so can remove it.
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://lore.kernel.org/r/20230726143141.11704-1-yuehaibing@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/bridge/br_private.h

@@ -974,7 +974,6 @@ int br_multicast_set_vlan_router(struct net_bridge_vlan *v, u8 mcast_router);
 int br_multicast_toggle(struct net_bridge *br, unsigned long val,
 			struct netlink_ext_ack *extack);
 int br_multicast_set_querier(struct net_bridge_mcast *brmctx, unsigned long val);
-int br_multicast_set_hash_max(struct net_bridge *br, unsigned long val);
 int br_multicast_set_igmp_version(struct net_bridge_mcast *brmctx,
 				  unsigned long val);
 #if IS_ENABLED(CONFIG_IPV6)