Revert "nvme: create 'slaves' and 'holders' entries for hidden controllers"

This reverts commit e9a48034.

The slaves and holders link for the hidden gendisks confuse lsblk so that
it errors out on, or doesn't report the nvme multipath devices.  Given
that we don't need holder relationships for something that can't even be
directly accessed we should just stop creating those links.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reported-by: Potnuri Bharat Teja <bharat@chelsio.com>
Cc: stable@vger.kernel.org
Signed-off-by: Keith Busch <keith.busch@intel.com>