This removes the EventListener, EventInit and CustomEventInit constructors from the userland globals. The type exports stay.
I removed the internal classes as well. EventListener's implementation seemed to be doing some bookkeeping on handled events but that's not being used anywhere so I assume it's old debug stuff. The other two are completely redundant.
A major API change was that asserts are imported from testing/asserts.ts
now rather than testing/mod.ts and assertEqual as renamed to
assertEquals to conform to what is most common in JavaScript.
