Exercises are listed on website despite not being in `config.json` nor `exercises/concept` about julia

[ErikSchierboom]

I'm positive we don't parse the wip config.json file. The reason the exercises are all listed is because:

1. They were once in the config.json file (see 9afbde5#diff-587cb980af76fdc7e52369fd0b9d926dff266976b6f8ac631e358fecc49ff8cf)
2. We don't support deleting exercises, only deprecating (so they aren't removed)
3. You're a maintainer so you see all exercises

[SaschaMann]

As a result, leap exists more than once (both in it's to-be-deprecated practice form and it's new concept form) and somehow multiplies if you click on it:

[ErikSchierboom]

The leap thing is weird, but likely due to it re-using the same slug (another reason why we don't want to re-use the exercises). If you've ever done the leap practice exercise, deprecating it will still result in it being shown.

[SaschaMann]

Ahh okay. I didn't know that it'd not remove them.