nfsd: remove redundant declarations

This is a cleanup patch. Functions nfsd_pool_stats_open() and
nfsd_pool_stats_release() are declared in fs/nfsd/nfsd.h.

Signed-off-by: Stanislav Kinsbursky <skinsbursky@parallels.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>