I thought this may have been part of fixing a sb2 -> sb3 corruption issue.
But from commit log, it seems this was added to prevent extensions from making mistakes.
With the scratch-parser change, those mistakes are now considered features.
Seems safe to just do remove these checks all the time.
Closes https://github.com/TurboWarp/scratch-vm/pull/332
Promise.reject() is not a constructor.
Additionally, rejecting with an Error instead of a string means
developer tools can show proper stack information.
Related to #82
Thomas Weber