Clean up experimental APNs related logic

[hjiangsu]

Pull Request Description

This PR removes the previous APNs implementation for push notifications on Apple devices. The main reason for this is to clean up the codebase a bit further, and remove the push submodule from the project. The APNs implementation was never completed, so removing this shouldn't have any side effects.

I'll likely revisit this in the future when Lemmy adds better support for push notifications

Additionally, this PR also provides a fix to #1953

Issue Being Fixed

Issue Number: N/A

Screenshots / Recordings

Checklist

• If a new package was added, did you ensure it uses an appropriate license and is actively maintained?
• Did you use localized strings (and added appropriate descriptions) where applicable?
• Did you add semanticLabels where applicable for accessibility?