Reduce configuration of UnusedPrivateMember's split rules

[BraisGabin]

Those allowedNames were copy&pasted when UnusedPrivateMember was splitted. But some of them have no sense in some usages.

This is a follow up of #5722

[TWiStErRob]

feels like _ should be a parameter name, i.e.

foo.bar { _, x -> ... }

[BraisGabin]

It does... we could open an issue and move that to the other rule.

also I created this test case and we have a lot of false negatives regarding lambdas:

Pair(1, 2).let { (x, y) -> println(y) }
listOf<Int>().map { x -> 1 }.fold(a) { x, y -> y }
val foo: (String, String) -> Unit = { x, y -> println(y) }

And I think that we don't even should configure _ as an unused parameter. That's exactly the reason _ exists.

[TWiStErRob]

Yes, but otherwise it would be a false positive, isn't it?

I didn't know there were so many gaps, my point was that you added _ as private property, but not for parameter names, now I tried and it's not allowed:

so it's pretty much only allowed as a lambda parameter.

[TWiStErRob]

@BraisGabin based on ^, it looks like we should just remove the _ exception.

[BraisGabin]

I didn't remove it from the property rule because, otherwise, we have false positives right now. We should probably take a look at it. I don't think the lambda check should be in the property rule and I think that we should omit those by default. But that's an improvement out of scope for this PR.

[TWiStErRob]

Ah, I see, the lambda param is a "private property", sorry, I missed that.

[TWiStErRob]

I was wondering why these were set up the the way they are. Nice one 👏