umount.cifs: don't build it by default

umount.cifs: don't build it by default

Now that the sanity checks for mount.cifs default to matching the
behavior of /bin/mount, then there is virtually no need for umount.cifs.
The only exception is when someone enables the loose setuid behavior in
mount.cifs.

If an unprivileged user mounts a share that isn't in /etc/fstab, then
/bin/mount won't allow that user to unmount it. In that situation,
umount.cifs will be necessary to allow unmounting the share.

Signed-off-by: Jeff Layton <jlayton@samba.org>
Acked-by: Steve French <smfrench@us.ibm.com>