Remove the help text below date filters on the Order backoffice view

In #1705950: Add visual styling to order listing request that we remove the "E.g., 2012-08-15" text from below the date filters.

This will need to be done in a date patch, because it's added in a #process callback:

  // TODO, figure out exactly when we want this description. In many places it is not desired.
  $sub_element['#description'] = ' '. t('E.g., @date', array('@date' => date_format_date(date_example_date(), 'custom', date_popup_date_format($element))));

So perhaps we just make it configurable (on / off setting?)