A long time ago, the Wikibase data model apparently knew a fourth rank: “truth”. This was deprecated and removed somewhere between 2014 and 2015, but still survives in the `mw.wikibase.entity` module as one of the available `claimRanks`. We should probably get rid of it there.
Unfortunately, though, it’s used in several modules (many of them copy+pasted, it seems):
```
lucaswerkmeister-wmde@mwmaint1002:~$ mwgrep --module RANK_TRUTH
brwikisource Module:Central-fr-ws
brwikisource Module:Centralizer
dewikisource Module:Central-s-de
elwiki Module:Carte interactive
eswikisource Module:Central-s-es
frwiki Module:Carte interactive
frwiki Module:Central
frwiki Module:Central-s-fr
frwiki Module:Centralizer
frwiki Module:ControlArgs
frwiki Module:Tests
frwikisource Module:Tests
frwikisource Module:Tpt
frwikiversity Module:Centralizer
huwiki Module:Central-w-hu
mediawikiwiki Module:Central
mediawikiwiki Module:Central-mw-en
test2wiki Module:ControlArgs
viwiki Module:Centralizer
(total: 19, shown: 19)
```
Some of those might be okay if `mw.wikibase.entity.claimRanks.RANK_TRUTH` turns into `nil`, but I haven’t checked all of them.