Uninstall of panels_mini depends on panels.module

panels_mini's hook_uninstall() depends on code that exists in panels.module: panels_delete_display(). The panels_node module does not have this dependency, simply because that module doesn't delete the displays associated with its panels.

There are two options to solve this:
1) Don't let panels_mini delete the associated displays.
2) Include panels.module conditionally:

    if (!function_exists('panels_delete_display')) {
      require_once drupal_get_path('module', 'panels') .'/panels.module';
    }

It's been too long since I've looked at Panels code, so I'm leaving this up to you, merlin.