[mediacapture-image] Pull Request: Remove invalid [Throws] extended attribute

dontcallmedom has just submitted a new pull request for 
https://github.com/w3c/mediacapture-image:

== Remove invalid [Throws] extended attribute ==
[Throws] is no longer a valid WebIDL extended attribute. In any case, 
it would not be applicable to a promise-returning function.

See https://github.com/w3c/mediacapture-image/pull/48