breaking: remove deprecated AppCache settings

[NiklasMerz]

Platforms affected

Android

Motivation and Context

The App Cache API will soon be removed: https://web.dev/appcache-removal/

The app cache methods for WebSettings are another thing that get deprecated for API level 30: https://developer.android.com/reference/android/webkit/WebSettings#setAppCacheEnabled(boolean)

Description

The app cache web API is considered deprecated and will get removed from Chrome/the Android webview around April 2021. Service workers are considered an alternative.

Testing

Unit tests

Checklist

• I've run the tests to see all new and existing tests pass
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary