block: restore /proc/partitions to not display non-partitionable removable devices

We found with newer kernels we started seeing the cdrom device showing
up in /proc/partitions, but it was not there before.

Looking into this I found that commit d27769ec

 ("block: add
GENHD_FL_NO_PART_SCAN") introduces this change in behavior.  It's not
clear to me from the commit's changelog if this change was intentional or
not.  This comment still remains: /* Don't show non-partitionable
removeable devices or empty devices */ so I've decided to send a patch to
restore the behavior of not printing unpartitionable removable devices.

Signed-off-by: Josh Hunt <johunt@akamai.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>