MigrateControllerTest requires root user, remove @todo

Problem/Motivation

\Drupal\Tests\migrate_drupal_ui\Functional\MigrateControllerTest has an @todo to remove the use of the root user but migrations through the UI must be run as the root user.

See \Drupal\migrate_drupal_ui\MigrateAccessCheck::checkAccess

Steps to reproduce

Proposed resolution

Remove the following lines:

   *
   * @todo Remove and fix test to not rely on super user.
   * @see https://www.drupal.org/project/drupal/issues/3437620

See #3439901-8: Fix Migrate Drupal UI tests that rely on UID1's super user behavior for confirmation of this solution.

Remaining tasks

Create MR
Review
Commit

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet