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.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>