blocks: remove BlockIcon wrapper in multiple blocks.

[jeherve]

Follow-up from #13324

Changes proposed in this Pull Request:

All of these are passed as an icon prop to Placeholder components, which accepts a string, or ReactElement.

Jetpack product discussion

• N/A

Does this pull request change what data or activity we track or use?

• No

Testing instructions:

• check all those blocks in the editor, the icons should be displayed everywhere.
• Ensure that the icons are still styled properly, that no added margin / padding appear (see Tiled gallery & Slideshow: use BlockIcon component in mediaPlaceholders #12160)

[matticbot]

Caution: This PR has changes that must be merged to WordPress.com
Hello jeherve! These changes need to be synced to WordPress.com - If you 're an a11n, please commandeer and confirm D74154-code works as expected before merging this PR. Once this PR is merged, please commit the changes to WP.com. Thank you!
This revision will be updated with each commit to this PR

[github-actions]

Thank you for your PR!

When contributing to Jetpack, we have a few suggestions that can help us test and review your patch:

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Jetpack plugin:

• Next scheduled release: March 1, 2022.
• Scheduled code freeze: February 22, 2022.

[sdixon194]

Things look good to me here as far as my testing goes 👍

[github-actions]

Great news! One last step: head over to your WordPress.com diff, D74154-code, and commit it.
Once you've done so, come back to this PR and add a comment with your changeset ID.

Thank you!

[jeherve]

r239726-wpcom