Thinking about this and considering some recent events, I imagine that a removal out of the blue may have the potentiality to break filters using these variables. This means that we need at least to run a query for every use case of these two variables and remove them from filters. For the moment, a good point would be to hide them from dumped vars, since showing them doesn't bring any benefit to users. I'll send a patch for this in (hopefully) a couple of minutes.

Change 425529 had a related patch set uploaded (by Daimona Eaytoy; owner: Daimona Eaytoy):
[mediawiki/extensions/AbuseFilter@master] Hide disabled vars from dumps

https://gerrit.wikimedia.org/r/425529

Actually, we can't remove them completely. What we can do is hide them per reasons above, and stop computing them for new edits, while keeping them in old logs where they were computed.

Change 430905 had a related patch set uploaded (by Daimona Eaytoy; owner: Daimona Eaytoy):
[mediawiki/extensions/AbuseFilter@master] [WIP] Stop computing removed variables and show custom error message

https://gerrit.wikimedia.org/r/430905

Change 425529 abandoned by Daimona Eaytoy:
Hide disabled vars from dumps

Reason:
Superseded by Ife168522e6b1d8eb94ebbb8a16ae8831ec1dc497

https://gerrit.wikimedia.org/r/425529

Change 430905 merged by jenkins-bot:
[mediawiki/extensions/AbuseFilter@master] Stop computing removed variables and show custom error message

https://gerrit.wikimedia.org/r/430905