v3.2-dev: Revert addition of description field on media-type #5593

We merged in a pull request in #5584 that adds a new field to the specification, that would be published in a patch release. We shouldn't have added a field at this point BUT it would have been the right thing to do and the change is correctly included in v3.3 already.

To fix this issue, revert the PR that added the field to the specification and update the schemas in the 3.2 branch to match (and their tests!)