private function removeObsoleteMetadata(): void
  {
    // 1 pass through $mySources make new array with routine_name is key.
    $clean = [];
    foreach ($this->sources as $source)
    {
      $routine_name = $source['routine_name'];
      if (isset($this->phpStratumMetadata[$routine_name]))
      {
        $clean[$routine_name] = $this->phpStratumMetadata[$routine_name];
      }
    }

    $this->phpStratumMetadata = $clean;
  }