Deprecate yoast_plugin_compatibility_notification and related code

[IreneStr]

Summary

This PR can be summarized in the following changelog entry:

• Removes the notification that would be thrown if add-ons with a lower version number than the plugin were installed. The yoast_plugin_compatibility_notification method has been deprecated.

Relevant technical choices:

Test instructions

This PR can be tested by following these steps:

• Install add-on versions below 12.2.
• Install the Yoast test helper.
• Go to trunk (or if RC-testing: use a pre-12.3 zip) of wordpress-seo. Build everything, and go to the Yoast Notification center. See that there are notifications under Problems about old add-on versions.
• Switch to this branch.
• If acceptance testing this: change if ( version_compare( $version, '12.3-RC0', '<' ) ) { in inc/class-upgrade.php to if ( version_compare( $version, '12.1-RC0', '<' ) ) {
  • You don't need to do this step if you're RC-testing the 12.3-RCx zip.
• In the test helper, set the database to an old version, e.g. 10.0, and click save. This will trigger the upgrade routine.
• Go back to the dashboard and see that the notifications are gone.

UI changes

• This PR changes the UI in the plugin. I have added the 'UI change' 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
• I have added unittests to verify the code works as intended

Fixes #13485

[igorschoester]

Acceptance ✅