This PR removes the old legacy standard claims, which have been deprecated since the beginning of the `v4` module in favor of the newer `RegisteredClaims`. Removing them before any further changes to the validation API is quite useful, as less code needs to be adapated.
This commit serves as the basis for further `v5` developments. It will introduce some API-breaking changes, especially to the way tokens are validated. This will allow us to provide some long-wanted features with regards to the validation API. We are aiming to do this as smoothly as possible, however, with any major version. please expect that you might need to adapt your code.
The actual development will be done in the course of the next week, if time permits. It will be done in seperate PRs that will use this PR as a base. Afterwards, we will probably merge this and release an initial 5.0.0-alpha1 or similar.