drop Sync req from setup and setup_with_config

[JonasKruckenberg]

What kind of change does this PR introduce?

• Bugfix
• Feature
• Docs
• New Binding issue #___
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change?

• Yes, and the changes were approved in issue #___
• No

Checklist

• When resolving issues, they are referenced in the PR's title (e.g fix: remove a typo, closes #___, #___)
• A change file is added if any packages will require a version bump due to this PR per the instructions in the readme.
• I have added a convincing reason for adding this feature, if necessary

Other information

Somehow this got lost during the previous PR. There is really no reason for SetupHook and SetupWithConfigHook.

1. The function gets called during App::plugin on the same Thread.
2. Even if we call it from a different thread, if the closure consumes owned references, those will not live past that closure and can't be shared between threads anyway. So the Sync requirement is redundant if I'm correct.