Replace open_count check with holders/mounted_fs check on lvremove path.

Replace open_count check with holders/mounted_fs check on lvremove path.

Before, we used to display "Can't remove open logical volume" which was
generic. There 3 possibilities of how a device could be opened:
  - used by another device
  - having a filesystem on that device which is mounted
  - opened directly by an application

With the help of sysfs info, we can distinguish the first two situations.
The third one will be subject to "remove retry" logic - if it's opened
quickly (e.g. a parallel scan from within a udev rule run), this will
finish quickly and we can remove it once it has finished. If it's a
legitimate application that keeps the device opened, we'll do our best
to remove the device, but we will fail finally after a few retries.