Postponed on #3113649: Remove drupal.tabbingmanager's jQueryUI dependency
Problem/Motivation
In #3113649: Remove drupal.tabbingmanager's jQueryUI dependency, jQuery UI tabbingmanager was shimmed so any uses of the :tabbable
selector do not invoke any code in jQuery UI's tabbable.js/tabbable-min.js.
Starting with comment #46 in that issue, there has been some debate regarding whether these no-longer-used-by-core jQuery UI files should be removed, and it's reached the point where that's the final item blocking the issue. Since removing those files is not critical to adding the new tabbable library+shim, this followup issue was created.
The comments that discuss including/removing the files: #46-#52, #77-#78, #83