Remove e-notice causing clause.

I'm pretty convinced that this would never be true - although it WOULD be true [] would have the case fields. We are calling queryFields both with case enabled & disabled which is the only thing changing it's output

CRM/Export/BAO/Export.php

@@ -1729,9 +1729,6 @@ public static function setHeaderRows($field, $headerRows, $sqlColumns, $processo
     elseif ($field == 'provider_id') {
       $headerRows[] = ts('IM Service Provider');
     }
-    elseif (substr($field, 0, 5) == 'case_' && $queryFields['case'][$field]['title']) {
-      $headerRows[] = $queryFields['case'][$field]['title'];
-    }
     elseif (array_key_exists($field, self::$relationshipTypes)) {
       foreach ($value as $relationField => $relationValue) {
         // below block is same as primary block (duplicate)