Trying to fix errores with the admin_menu module
Admin menu hasn't had any development effort for comfortably more than 2 years now. It doesn't have a Drupal 8 release to speak of; the chances of getting the module working without major surgery to the code are pretty slim.

If you can get the module successfully uninstalled by commenting out some code, then definitely do it (then probably delete the module folder so you don't accidentally enable it again).

The Admin Toolbar module is its successor. It integrates with the core toolbar, and has a sub-module which provides the tools menu that you'll be familiar with from Drupal 7 (with clear cache links etc).