Remove unnecessary SchedulingViewControllerProtocol

[mokagio]

This protocol used to be a facade between SchedulingDatePickerViewController and SchedulingCalendarViewController but the latter has been removed in a60d3d9 during the iOS 13 Widgets removal so we can remove the abstraction.

Testing

If CI builds, we're good to go.

Regression Notes

1. Potential unintended areas of impact – N.A.
2. What I did to test those areas of impact (or what existing automated tests I relied on) – N.A.
3. What automated tests I added (or what prevented me from doing so) – N.A.

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

[wpmobilebot]

You can test the changes in Jetpack from this Pull Request by:

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[wpmobilebot]

You can test the changes in WordPress from this Pull Request by:

• Clicking here or scanning the QR code below to access App Center
• Then installing the build number pr19708-20df412 on your iPhone

If you need access to App Center, please ask a maintainer to add you.

[joshheald]

Code looks good. I've not tested it though as I don't have a WPiOS dev env set up right now: I added this on a maintenance rotation. Since it's building, I expect it's fine.

[joshheald]

Perhaps this can be removed as well? I can think of arguments for or against, so either way is good with me, but just checking whether you've considered it.

[mokagio]

Good catch. I should have mentioned that I left that for #19709 . Thanks!