Remove hard-coded theme_X calls.

theme_X functions should never be called directly. Rather, they should be called like:

theme('X', $stuff);

so that they use Drupal's theme override mechanism.

So for example, in quiz_view:

    $node->body = theme_quiz_view(&$node, $teaser, $page);

should be:

    $node->body = theme('quiz_view', &$node, $teaser, $page);