ipvs: remove unused seqcount stats

 	Remove ustats_seq, IPVS_STAT_INC and IPVS_STAT_ADD
because they are not used. They were replaced with u64_stats.

Signed-off-by: Julian Anastasov <ja@ssi.bg>
Signed-off-by: Simon Horman <horms@verge.net.au>