uninstall tries to remove variables from the "variables" table and fatals

The uninstall tries to remove from old 6.x style "variables" table, needs upgrading to 7.x "variable"

function gpui_uninstall() {
  // Remove the parsed source code directory.
  $dir = gpui_directory_path('parser', FALSE);
  gpui_clean_directory($dir, TRUE);

  // Remove items from {variables} table.
  db_delete('variables')
    ->condition('name', db_like('gpui_') . '%', 'LIKE')
    ->execute();
}

one line fix. at line 32 of gpui.install:

 db_delete('variable')