refactor(App): \OC\AppFramework\App clean-up

[joshtrichards]

• Resolves: #n/a

Summary

• Dead code removal:
  • part() method
    • not used anywhere
    • has also been broken for >10 years (since the return layout array changed on dispatcher())
    • Ref: 0481390
• Code formatting

TODO

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)