net: llc: Remove unused function declarations

llc_conn_ac_send_i_rsp_as_ack() and llc_conn_ev_sendack_tmr_exp()
are never implemented since beginning of git history.

Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20230803134747.41512-1-yuehaibing@huawei.com


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