NFS: Remove nfs4_setup_sequence from generic unlink code

This is an NFS v4 specific operation, so it belongs in the NFS v4 code
and not the generic client.

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