Re-enable no-unused-expressions rule

[markelog]

It was disabled because of the cases like this -
https://github.com/jquery/jquery/blob/93f706200c6101df137469ba2e0d965e93508991/src/css/showHide.js#L21

But it seems like it is an issue with our code and with eslint too - eslint/eslint#6636

[platinumazure]

I've left a comment on the ESLint issue. I don't think the logic should change (and I would consider the "violations" to be actual code style issues, in my opinion), but I think the error message could be improved.

In the meanwhile, would it help for someone to submit a PR to jQuery and other projects fixing those issues? (One could just turn the rule on locally and replace the commas with semicolons, basically, and then commit the fixes without enabling the rule.)

[markelog]

would it help for someone to submit a PR to jQuery and other projects fixing those issues?

I already did that, no worries