net/smc: Remove unused function declaration

The declaration of smc_wr_tx_dismiss_slots() is unused.
So remove it.

Fixes: 349d4312 ("net/smc: fix kernel panic caused by race of smc_sock")
Signed-off-by: Wen Gu <guwen@linux.alibaba.com>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>