message: event: remove unneeded ASSERT.
  This should now be fixed in
  Risk level: Low
  Testing: CI (previously verified in the libevent work that the fix
  worked).
diff: @@ -62,12 +62,8 @@ void FileEventImpl::assignEvents(uint32_t events, event_base* base) {
  events |= FileReadyType::Closed;
  }
  - // TODO(htuch): this should be ASSERT(events), but
  - // https://github.com/libevent/libevent/issues/984 seems to be producing unexpected
  - // behavior. The ASSERT should be restored once this issue is resolved.
  - if (events) {
  + ASSERT(events != 0);
  event->cb_(events);
  - }
  },
  this);
  }
  