Classic Block: Remove conversion from BlockInvalidWarning

[tyxla]

What?

Removes the Convert to Classic Block option from the invalid block warning (BlockInvalidWarning).

Why?

The classic (core/freeform) block is being de-emphasized and is hidden from the modern inserter. Offering "Convert to Classic Block" as a resolution for an invalid block steers users toward a legacy block we no longer want to promote. The remaining options — Attempt recovery, Resolve, and Convert to HTML — cover the relevant recovery paths.

Part of #78067.

How?

In packages/block-editor/src/components/block-list/block-invalid-warning.js:

• Drop the canInsertClassicBlock selector (the canInsertBlockType( 'core/freeform', … ) check).
• Remove the convert.toClassic() converter that created a core/freeform block.
• Remove the "Convert to Classic Block" entry from secondaryActions.
• Update both useSelect and useMemo dependency arrays accordingly.

Testing Instructions

1. Open the editor for a new post.
2. Open the Code editor (Options menu → Code editor) and paste a block with tampered/invalid markup, e.g.:

   <!-- wp:paragraph -->
   <p>Hello <strong>world</strong></p>
   <div>unexpected extra markup</div>
   <!-- /wp:paragraph -->

3. Switch back to the Visual editor. The block shows "Block contains unexpected or invalid content."
4. Open the warning's secondary actions.
5. Expected: You see Resolve and Convert to HTML, but no "Convert to Classic Block" option.

Testing Instructions for Keyboard

Same

Screenshots or screencast

Before	After

Use of AI Tools

This PR was authored with assistance from Claude Code. All code was reviewed by the author before submission.

[github-actions]

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Co-authored-by: tyxla <tyxla@git.wordpress.org>
Co-authored-by: Mamaduka <mamaduka@git.wordpress.org>

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[github-actions]

Size Change: -59 B (0%)

Total Size: 7.51 MB

📦 View Changed

Filename	Size	Change
build/scripts/block-editor/index.min.js	382 kB	-59 B (-0.02%)

_{compressed-size-action}

[github-actions]

Flaky tests detected in 2c2998a.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/28115870488
📝 Reported issues:

• [Flaky Test] Should save the changes #78689 in /test/e2e/specs/editor/plugins/wp-editor-meta-box.spec.js

[Mamaduka]

Makes sense!