greylisting: drop unneeded Host column form cgreylist table

greylisting: drop unneeded Host column form cgreylist table

With the changes added in f61d54891d4820b21ef9e53f7ce0ebb1d5be1f73
greylisting does the matches based on a configurable netmask, and
does not use the 'Host' column in the cgreylist table anymore.

Drop it now with PMG 7.0

Quickly tested the following scenarios (all successfully):
* Upgrading from a previous version
* Restoring a pmg-backup taken with PMG 5.2 (the greylist table is
  excluded from the backup)
* Adding a node with the changes to an existing cluster without the
  change
* Adding a node without the changes to a master-node having them

Signed-off-by: Stoiko Ivanov <s.ivanov@proxmox.com>
Reviewed-By: Dominik Csapak <d.csapak@proxmox.com>
Tested-By: Dominik Csapak <d.csapak@proxmox.com>