fix(block-theme): remove MJML image-caption filter moved to newsletters plugin

[chickenn00dle]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

The MJML image-caption component attributes filter (setting align=left and padding=0) was duplicated identically in both the block theme and classic theme. This code has been moved into the newsletters plugin renderer as a default in Automattic/newspack-newsletters#2078, so the duplicate in this theme is no longer needed.

Depends on Automattic/newspack-newsletters#2078

Addresses https://linear.app/a8c/issue/NPPD-1316

How to test the changes in this Pull Request:

1. Apply fix(block-theme): override theme.json styles in the newsletter editor newspack-newsletters#2078 first
2. Activate the Newspack Block Theme
3. Create a Newsletter post with all of the non-RDB blocks (I decided not to tackle these here as this one is already quite hairy) listed in this comment
4. Send a test email and verify the image caption is left-aligned with no extra padding — same as before this change

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Removes a now-duplicated MJML image-caption component attributes filter from the block theme, based on the behavior being moved into the Newspack Newsletters plugin renderer.

Changes:

• Stops registering the newspack_newsletters_mjml_component_attributes filter in the theme.
• Removes the theme’s mjml_component_attributes() implementation that forced align=left and padding=0 for image-caption.

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[laurelfulford]

Looks good! Caption alignment still works with this PR + Automattic/newspack-newsletters#2078 😄