SERVER-10566 Inline MatchableDocument destructor

Allows subclasses to see that it is a no-op and avoid a function call.
SERVER-11711 Make aggregation/testall.js not depend on document order

Needed to make tests pass with agg on top of new query framework. The order of fields returned by
the new query framework is undefined due to SERVER-11833.
SERVER-11711 Make agg use new query framework