homework: get rid of manual clean up path in home_setup_luks()

homework: get rid of manual clean up path in home_setup_luks()

Now that we stored all our different objects inside the HomeSetup
structure, we can get rid of our manual clean-up path, since
home_setup_done() will clean up everything stored therein anyway, in the
right order.

This is the main reason we moved everything into HomeSetup in the
previous commits: so that we can share clean-up paths for these objects
with everything else.