HKDF-CTR replaced by HKDF

[ehuggett]

It would appear the algorithm was changed from NIST SP 800-108 to IETF RFC 5869, and it was renamed to HKDF (so HKDF-CTR is no longer part of the standard?). w3c/webcrypto#27

Would it be better to replace the HKDF-CTR example or somehow mark it as obsolete and add a HKDF example separately?

example: https://github.com/mozilla/send/blob/9410defab6156d29bb705f73aefbd09ec588678e/app/fileSender.js#L126-L140 (does not use the Salt)