Revert "Restore the correct domain before calling the user callback"

This reverts commit b9175a2c0c397cf35903fcf7021bacac408b5edc.

Domains have been a common source of problems since I started using them and with
reports of memory leaks that got introduced in the latest version I think it's
save to say that this does not belong in this module and should be solved in
user code instead.

Fixes #186