Remove unnecessary compatibility shim added in 5.8

[desrosj]

It looks like a compatibility shim from the Gutenberg plugin has accidentally made its way into Core.

The inline documentation indicates that the code block allows the plugin to work with older versions of WordPress until 5.8 is made the minimum required version. This doesn't matter in the context of WordPress because this code is being added in 5.8.

[jorbin]

This looks good to be committed and backported

[desrosj]

Going to hold off committing to allow for additional context. See ​this thread in Slack.

[oandregal]

Hey, sorry about the late response. This code needs to remain, although the comment could be removed as it's a leftover.

This is what I've tested:

• Theme without theme.json support: the spacing panel is shown when the theme adds add_theme_support( 'custom-spacing' );, otherwise is not.

• Theme with theme.json and settings.spacing.customPadding equals true: the spacing panel is shown, whether or not the theme has custom-spacing theme support.

• Theme with theme.json and settings.spacing.customPadding equals false: the spacing panel is not shown, whether or not the theme has custom-spacing theme support.

I've also tested that it can be enabled per block (disable the top-level settings.spacing.customPadding but enable it for the core/cover block, for example).

[desrosj]

In 51352:

Themes: Remove inline comment that is not relevant in WordPress Core.

This removes an inline comment block that was added when importing the WP_Theme_JSON class in [50959]. The comment is relevant to the code only when viewed within the context of the Gutenberg plugin.

Props nosolosw, jorbin.
Fixes #53576.

[desrosj]

Thanks @nosolosw!

I've verified your testing steps and I'm seeing the same thing.

Conclusion: the inline comment is specific to the Gutenberg plugin, but only because the code following the notice will not be in WordPress Core until 5.8.

I've removed the inline comment in [51352] and marking for backport.

[SergeyBiryukov]

Looks good to backport.

[desrosj]

In 51364:

Themes: Remove inline comment that is not relevant in WordPress Core.

This removes an inline comment block that was added when importing the WP_Theme_JSON class in [50959]. The comment is relevant to the code only when viewed within the context of the Gutenberg plugin.

Props nosolosw, jorbin, SergeyBiryukov.
Merges [51352] to the 5.8 branch.
Fixes #53576.