Stumbled on this while trying to install the "new" appimaged (go-appimage).
Apparently sudo apt remove --purge appimagelauncher
isn't good enough.
Need to manually remove remnants of broken links for appimagelauncherd (and appimagelaunchefs) under ~/.config/systemd/user and ~/.config/systemd/user/default.target.wants.
Also, any appimagelauncher* files under ~/.config as well. Also see appimaged README.
Then you can move on.
https://github.com/probonopd/go-appimage/blob/master/src/appimaged/README.md