Remove FeatureFlag.modernizeMedia and associated code

[kean]

To test:

• Verify that Site Media screens opens
• Verify that Site Media pickers in Gutenberg, Site Icon flow, and Feature Image flow allow you to select images from Site Media

I wish I could remove more, but Aztec and Story Editor use WPMediaPicker and I'm hoping we get to the point where both can be removed.

Regression Notes

1. Potential unintended areas of impact: n/a (only removal)
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

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]

	1 Warning
⚠️	This PR is larger than 500 lines of changes. Please consider splitting it into smaller PRs for easier and faster reviews.

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[wpmobilebot]

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	App Name	WordPress Alpha
	Configuration	Release-Alpha
	Build Number	pr22040-7e98069
	Version	23.6
	Bundle ID	org.wordpress.alpha
	Commit	7e98069
	App Center Build	WPiOS - One-Offs #7838

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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	pr22040-7e98069
	Version	23.6
	Bundle ID	com.jetpack.alpha
	Commit	7e98069
	App Center Build	jetpack-installable-builds #6864

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[crazytonyli]

Nice work! Glad to see that many legacy code got removed.

[crazytonyli]

@kean I have found a bug in adding images. It's probably not related to this PR though.

1. Add a gallery block in Gutenburg editor.
2. Tap add media.
3. Select multiple images and then tap the Cancel button.

The selected images are added to the editor. But they should not be.

[kean]

The selected images are added to the editor. But they should not be.

Nice catch, thanks! Yes, I can reproduce it in my branch. It looks like an issue in the new Site Media view controller. I'll open a PR with a fix targeting the 23.7 release branch.

[kean]

Fix #22041