POSTPONED: As long as we support IE11, these role attributes are staying. Detailed explanation in comment #14
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This is a follow-up of #2467827: [META] W3C validation for Drupal Core
Drupal core added a lot of WAI-ARIA roles to Drupal core (which is a good thing), but in the process lots of unneeded duplicates are added as well.
A WAI-ARIA role is needed when the markup itself isn't clear. But markup like and is superfluous since the HTML elements themselves already explain their role. Having these (duplicate) attributes makes W3C validation fail and we don't want that.