[SCTP]: Kill unused static inline sctp_sysctl_jiffies_ms

After the patch:
$ git-grep sctp_sysctl_jiffies_ms | wc -l
0

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Acked-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>