cifs: remove rw/ro options

cifs: remove rw/ro options

These options are handled at the VFS layer. They only ever set the
option in the smb_vol struct. Nothing was ever done with them afterward
anyway.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>