Clean up theme_dvg_appointments_date_time()

The images are currently missing. I guess it 's best to remove them altogether and leave that up to CSS.

        $day_part_status = array(
          TRUE => array(
            'icon' => 'icon-tick.png',
            'alt' => t('available'),
          ),
          FALSE => array(
            'icon' => 'icon-cross.png',
            'alt' => t('unavailable'),
          ),
        );
        $image = array(
          'path' => drupal_get_path('module', 'appointments') . '/images/' . $day_part_status[$day_part_available]['icon'],
          'alt' => $day_part_status[$day_part_available]['alt'],
        );
        $day_part_image = '<span class="day-part-image ' . $image_class . '">' . theme('image', $image) . '</span>';
        $day_part_content = '<div class="day-part">' . $day_part_prefix . ' ' . $day_part_image . '</div>';