@jsotuyod The build is failing because the old deprecated rulesets (eg codesize.xml) reference inexistent rules now. Can I remove them in this PR too? I don't see the point of fixing the files only to remove them later on. Let's do that later

At some point before releasing pmd 7, we need to delete the pmd 5 rulesets, which are all deprecated.
We might deprecate more rules until we release pmd 7 (like UseObjectForClearerApi, SimplifyStartsWith - see https://github.com/pmd/pmd/wiki/PMD-7.0.0). Not sure however, whether we would directly remove these rules with pmd 7 - but I think, that's ok, because it's a major version change.
For removing the old rulesets, we need to consider the other languages as well (not only apex and java).

Oh, and before actually deleting these "unlinked/unused" rules, we should collect them, if they sound useful, to have suggestions for new rules (see also https://github.com/pmd/pmd/wiki/Project-Ideas-%5BMature%5D#new-rules) - even if we don't implement them now.

@adangel I think it's ok to remove rules that were not necessarily deprecated for 7.0.x. I think though, that it would be nice for rules that are not found to cause a warning instead of a ruleset parsing error. At the very least, we should collect all failures and present them all to the user instead of one by one. This will make version transitions smoother for the user

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