Changes:
* Use ECMAScript class and arrow function syntax for Tracker.Computation
and Tracker.Dependency.
* Remove the deprecated.js file (no more Deps, Tracker.depend, or
Tracker-related Meteor.* APIs).
* Set stopped computation to null instead of delete (#7326)
Delete can be very slow. Setting the stopped computation property to null instead brings a speed gain of 3-10x.
http://bertanguven.com/preventing-memory-leaks-in-javascript-null-vs-delete
* add generated npm-shrinkwrap.json
* Remove computation tracking from Tracker.
Tracker.flush() will still guarantee that all computations and
afterFlush callbacks have been fully flushed, but the implicit flush
cycle started by an invalidation or afterFlush call will yield to the
event loop for 10ms every thousand computations.
Fixes#3901.
Reviewed at https://rbcommons.com/s/meteor/r/25/