[NETFILTER]: ipt_CLUSTERIP: kill clusterip_config_entry_get

It's unused static inline.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>