Remove old configurations

[BraisGabin]

I'm opening this as a PR but because it's easier than an Issue in this case.

I think that no one uses this configuration any more. It had sense when all/nearly all the rules didn't have type-solving. But right now configurations like that one have little sense.

If you use these configurations or you think it is worth to keep them just close this PR :)

[schalkms]

Is the file statistics.yaml still referenced somewhere in the code base? I know that a dogfooding approach was used to run detekt's statistic features on the detekt code base. I'm not sure whether we want to keep it.

I think the Gradle config could be removed quite safely.

[BraisGabin]

Is the file statistics.yaml still referenced somewhere in the code base? I know that a dogfooding approach was used to run detekt's statistic features on the detekt code base. I'm not sure whether we want to keep it.

I couldn't find any reference to statistics.yml (except the one that I removed).