Issue #2072589 by legolasbo: Remove Unused local variable from...

Issue #2072589 by legolasbo: Remove Unused local variable  from /core/modules/views/lib/Drupal/views/Plugin/views/join/Subquery.php.

core/modules/views/lib/Drupal/views/Plugin/views/join/Subquery.php

@@ -60,7 +60,6 @@ public function buildJoin($select_query, $table, $view_query) {
       if (is_array($this->extra)) {
         $extras = array();
         foreach ($this->extra as $info) {
-          $extra = '';
           // Figure out the table name. Remember, only use aliases provided
           // if at all possible.
           $join_table = '';