Code cleanup outdated addons tabs in metabox

[vraja-pro]

Context

• Clean unused code from old ui tabs for Yoast addons in metabox. See old UI

Summary

This PR can be summarized in the following changelog entry:

• Cleans old ui code for addons tabs in metabox.

Relevant technical choices:

• Added defensive coding to WPSEO_Meta:keyword_usage after seeing a warning.
• The relevant part of the UI was deprecated here

Test instructions

Test instructions for the acceptance test before the PR gets merged

This PR can be acceptance tested by following these steps:

• Install Yoast Video anf Yoast News
• Go to edit page or post and check metabox tabs are working.

Relevant test scenarios

• Changes should be tested with the browser console open
• Changes should be tested on different posts/pages/taxonomies/custom post types/custom taxonomies
• Changes should be tested on different editors (Block/Classic/Elementor/other)
• Changes should be tested on different browsers
• Changes should be tested on multisite

Test instructions for QA when the code is in the RC

• QA should use the same steps as above.

QA can test this PR by following these steps:

Impact check

This PR affects the following parts of the plugin, which may require extra testing:

UI changes

• This PR changes the UI in the plugin. I have added the 'UI change' label to this PR.

Other environments

• This PR also affects Shopify. I have added a changelog entry starting with [shopify-seo], added test instructions for Shopify and attached the Shopify label to this PR.

Documentation

• I have written documentation for this change.

Quality assurance

• I have tested this code to the best of my abilities.
• During testing, I had activated all plugins Yoast SEO provides integrations for.
• I have added unit tests to verify the code works as intended.
• If any part of the code is behind a feature flag, my test instructions also cover cases where the feature flag is switched off.
• I have written this PR in accordance with my team's definition of done.

Innovation

• No innovation project is applicable for this PR.
• This PR falls under an innovation project. I have attached the innovation label and noted the work hours.

Fixes #

[coveralls]

Pull Request Test Coverage Report for Build 5311202240

• 0 of 1 (0.0%) changed or added relevant line in 1 file are covered.
• 35 unchanged lines in 5 files lost coverage.
• Overall coverage increased (+0.04%) to 40.137%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
inc/class-wpseo-meta.php	0	1	0.0%

Files with Coverage Reduction	New Missed Lines	%
src/helpers/wincher-helper.php	1	60.87%
src/integrations/front-end-integration.php	3	75.51%
src/actions/wincher/wincher-account-action.php	5	40.91%
src/routes/wincher-route.php	6	44.04%
admin/watchers/class-slug-change-watcher.php	20	15.0%

Totals
Change from base Build 5209706808:	0.04%
Covered Lines:	9645
Relevant Lines:	24030

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💛 - Coveralls

[enricobattocchi]

A couple of suggestions

[enricobattocchi]

CR ok

[enricobattocchi]

ACC ok