Unnecessary `ext` folder

[grant]

The repo has a folder of the CE spec in JSON format in ext.

https://github.com/cloudevents/sdk-javascript/tree/master/ext

While this may be useful, it's not necessary for a CloudEvent SDK. Let's refer back to the spec rather than keeping the files.

[grant]

It looks like these specs might be currently used. I'll keep this open but close the PR.

[lance]

This issue is related to #96. The .json in ext/ is used to validate the data in an event using the AJV validator. I don't think this should be removed.

[grant]

Yes, it shouldn't be removed unless there is a replacement validator.

[lance]

Closing. Fixed in #129