only create users if pico-wizard is not installed

This makes the post install only create a user, if the pico-wizard binary is not installed.

This will effectively remove the manjaro/kde user from installs where pico-wizard sets up a custom user for the user anyway. So the manjaro/kde user is not needed.

It should also keep the user creation if pico-wizard is not installed, so Phosh and Lomori editions should still get the manjaro user.