nfsd: Drop including client's header file nfs_fs.h

nfs_fs.h is a client's header file.

# ll fs/nfsd/nfs4acl.o fs/nfsd/nfsd.ko
-rw-r--r--. 1 root root 328248 Jul  3 19:26 fs/nfsd/nfs4acl.o
-rw-r--r--. 1 root root 7452016 Jul  3 19:26 fs/nfsd/nfsd.ko

After this patch,
# ll fs/nfsd/nfs4acl.o fs/nfsd/nfsd.ko
-rw-r--r--. 1 root root 150872 Jul  3 19:15 fs/nfsd/nfs4acl.o
-rw-r--r--. 1 root root 7273792 Jul  3 19:23 fs/nfsd/nfsd.ko

Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>