Comments Block: Remove unnecessary editorStyle prop in legacy metadata

[DAreRodz]

What and why?

This PR removes an editorStyle property defined in the legacy Post Comments block's metadata.

Reasons:

1. the property is not correctly defined; it should be editor_style instead.
2. the property is not actually needed ―as mentioned here― because the legacy block is never rendered in the editor.

Note that nothing was going wrong from the user's perspective, so this fix could be considered a code-quality fix.

How?

Simply removing the offending line of code. 🙂

Testing Instructions

1. Install a theme that uses the old Post Comments block (e.g., TT1 Blocks)
2. Go to the Single template
3. Ensure that the block being rendered is the Comments block. You can do so by either:
   3.1. checking the class used by the rendered element (it should be wp-block-comments) or
   3.2. opening the code editor (the block markup should be <!-- wp:comments {"legacy":true} /--></div>
4. The styles used by the block come from editor.css and are applied correctly, with and without this PR.

Screenshots or screencast

This is how it should look, before and after.

[michalczaplinski]

Looks good to me! 👍