chore: remove more deprecated UIWebView things

[erisu]

Motivation, Context & Description

Cleanup repo to remove more things that are UIWebView related.

• Remove Preference:

  • GapBetweenPages
  • KeyboardDisplayRequiresUserAction
  • PageLength
  • PaginationBreakingMode
  • PaginationMode

• Removed gap: from template.

Testing

• N/A

Checklist

• [ ] I've run the tests to see all new and existing tests pass