nfs: remove unnecessary NFS_INO_INVALID_ACL checks

Unless I'm mistaken, NFS_INO_INVALID_ACL is being checked twice during
getacl calls (i.e. first via nfs_revalidate_inode() and then by each all
site).

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>