Issue #2189661 by tim.plunkett: Replace $form_state['redirect_route'] with setRedirect().

core/lib/Drupal/Core/Form/FormState.php

core/lib/Drupal/Core/Form/FormStateInterface.php

core/modules/action/src/ActionFormBase.php

core/modules/action/src/Form/ActionAdminManageForm.php

core/modules/action/src/Form/ActionDeleteForm.php

core/modules/aggregator/src/FeedForm.php

core/modules/aggregator/src/Form/FeedDeleteForm.php

core/modules/aggregator/src/Form/FeedItemsDeleteForm.php

core/modules/aggregator/src/Form/OpmlFeedAdd.php

core/modules/ban/src/Form/BanAdmin.php

core/modules/ban/src/Form/BanDelete.php

core/modules/block/src/BlockForm.php

core/modules/block/src/Form/BlockDeleteForm.php

core/modules/block_content/src/BlockContentForm.php

core/modules/block_content/src/BlockContentTypeForm.php

...modules/block_content/src/Form/BlockContentDeleteForm.php

...les/block_content/src/Form/BlockContentTypeDeleteForm.php

core/modules/book/src/Form/BookOutlineForm.php

core/modules/book/src/Form/BookRemoveForm.php

core/modules/comment/src/CommentForm.php