mount.nfs: /bin/mount already handles --bind & friends

Clean-up: remove logic to handle --bind and other such command-line
options from mount.nfs[4].

These options are already handled in /bin/mount, and the logic for handling
them in the NFS helper is currently disabled.  Other helpers such as
mount.ocfs2 appear not to support --bind (ie. they rely on /bin/mount to
do it).

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Neil Brown <neilb@suse.de>