Remove re-execution of buffered queries.

This solves incorrect results in SQLServer, as re-executing the query
would drop text columns for reasons I don't really understand. As
a side-effect loading associated data should be faster.

src/Database/Statement/BufferedStatement.php

@@ -302,9 +302,6 @@ public function current()
      */
     public function rewind()
     {
-        if (!$this->_hasExecuted) {
-            $this->execute();
-        }
         $this->index = 0;
     }