sources: Remove ABUSECH_BOTNETC2 from ipblocklist sources

sources: Remove ABUSECH_BOTNETC2 from ipblocklist sources

- Abuse.ch deprecated the ABUSECH_BOTNETC2 list on 3rd Jan 2025 without any warning or
   notification except for the deprecation message in the block list.
- This patch removes that list from the ipblocklist sources.
- This is part of a patch set that also removes this list from the files in users
   systems and from any restore from an earlier backup when the updates sources list is
   issued.

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>