Revert "Update more call sigs for mongoengine 0.8"

This reverts commit 41b0a16287eee25a0ff897882a9e3cd5fdbd37c4.
Revert "Update method signatures for mongoengine 0.8"

This reverts commit a61592ca16f8715f5b56afebc8a55f55a30f2cc4.