[Tests] Add back missing OneSignalUNUserNotificationCenterSwizzingTest and clean up dead test support files

[jkasten2]

Description

One Line Summary

Add back missing OneSignalUNUserNotificationCenterSwizzingTest test file in Xcode and delete some no longer used test support classes.

Details

Motivation

Make sure we don't skip important swizzing tests.

Scope

Just tests affected.

Affected code checklist

• Notifications
  • Display
  • Open
  • Push Processing
  • Confirm Deliveries
• Outcomes
• Sessions
• In-App Messaging
• REST API requests
• Public API changes
• Tests

Checklist

Overview

• I have filled out all REQUIRED sections above
• PR does one thing
• Any Public API changes are explained in the PR details and conform to existing APIs

Testing

• I have included test coverage for these changes, or explained why they are not needed
• All automated tests pass, or I explained why that is not possible
• I have personally tested this on my device, or explained why that is not possible

Final pass

• Code is as readable as possible.
• I have reviewed this PR myself, ensuring it meets each checklist item

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This change is 

[emawby]

Reviewed 1 of 5 files at r1.
Reviewable status: 1 of 5 files reviewed, all discussions resolved (waiting on @nan-li)