NFS: Remove support for the 'nfsprog' option

Remove the mount option that allows users to specify an alternate NFS
program number.  The client hasn't support setting an alternate NFS
program number for a very long time.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>