Fix an issue with scheduling of posts not working on iOS 17 with Xcode 15

[kean]

Fixes #21649

I removed PartScreenPresentationController because it was used only in one place, which is a good thing because it means no other parts of the app has this regression. There is a way to implement the same (or better) behavior using the new-ish native UISheetPresentationController. But I decided to err on the side of simplicity and show it as a simple default model screen.

To test:

• Follow the steps from the defect (requires Xcode 15!)
• Verify that changing the scheduled date for an outstanding scheduled post works

Simulator.Screen.Recording.-.iPhone.15.-.2023-11-09.at.07.59.16.mp4

Regression Notes

1. Potential unintended areas of impact: Scheduling Post
2. What I did to test those areas of impact (or what existing automated tests I relied on): manual
3. What automated tests I added (or what prevented me from doing so): n/a

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding unit tests for my changes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

UI Changes testing checklist:

• Portrait and landscape orientations.
• Light and dark modes.
• Fonts: Larger, smaller and bold text.
• High contrast.
• VoiceOver.
• Languages with large words or with letters/accents not frequently used in English.
• Right-to-left languages. (Even if translation isn’t complete, formatting should still respect the right-to-left layout)
• iPhone and iPad.
• Multi-tasking: Split view and Slide over. (iPad)

[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress Alpha by scanning the QR code below to install the corresponding build.

	App Name	WordPress Alpha
	Configuration	Release-Alpha
	Build Number	pr22012-97a612f
	Version	23.7
	Bundle ID	org.wordpress.alpha
	Commit	97a612f
	App Center Build	WPiOS - One-Offs #7884

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[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack Alpha by scanning the QR code below to install the corresponding build.

	App Name	Jetpack Alpha
	Configuration	Release-Alpha
	Build Number	pr22012-97a612f
	Version	23.7
	Bundle ID	com.jetpack.alpha
	Commit	97a612f
	App Center Build	jetpack-installable-builds #6908

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