http://concrete5-japan.org/community/forums/chat/post-10078/

app.php

<?php

use Concrete\Core\Workflow\Progress\PageProgress;
use Concrete\Core\Workflow\EmptyWorkflow;

Route::register('/clear_workflow_progress', function() {
    $list = PageProgress::getPendingWorkflowProgressList();
    $r = $list->get();
    foreach ($r as $w) {
        $wp = $w->getWorkflowProgressObject();
        $wo = $wp->getWorkflowObject();
        if ($wo instanceof EmptyWorkflow) {
            $wp->delete();
        }
    }
});