db.foo.remove({temporary: {$truthValue: true}})

Probably should share semantics (but not name) with BSONElement::trueValue() where 0, false, null, undefined, and missing are false and everything else is true. Alternatively we may want to treat empty Strings, Objects, and Arrays as false like python.

This can be approximated with an $in/$nin query, but I think it would be nice to have a proper query operator.