The only reason a callback was used, was so that the temporary directory
gets removed once `Build` returns. But that is honestly a really bad
reason: the parent function can simply create a temporary function and
remove it when it returns. It wasn't worth the code complexity that this
callback created.
This change should not cause any observable differences in behavior (it
should be a non-functional change).
I have no reason to do this now, but this unclean code has been bugging
me and I just wanted to get it fixed.
Ayke van Laethem
f866d5cc38