[mediacapture-output] Avoid Interface.attributeName notation

domenic has just created a new issue for 
https://github.com/w3c/mediacapture-output:

== Avoid Interface.attributeName notation ==
E.g. in the sentences

> If the HTMLMediaElement.sinkId is no longer present in the list of 
MediaDeviceInfo.deviceIds returned

This is confusing since sinkId is an instance property, not a static 
property. E.g. if you type `HTMLMediaElement.sinkId` in your browser 
console, the result will be undefined.

Instead say something like "the HTMLMediaElement's sinkId".

Please view or discuss this issue at 
https://github.com/w3c/mediacapture-output/issues/44 using your GitHub
 account