recipe.dropbear.AuthorizedKeysFile: Fix returned paths

This recipe only created ~/.ssh/authorized_keys, so it should not return the full ~/.ssh/ directory because uninstallation will delete "too much".

@alain.takoudjou @rafael after machine was restarted yesterday, the keys I added in ~/.ssh/ of my webrunner were not here anymore. I think this is the reason, thanks for taking a look when you have time.