Move owner set manipulation during document discarding

[domenic]

This is a small editorial change suggestion. Probably a good first bug, although I'd prefer @annevk sign off on the idea beforehand, so assigning it to him for a spot-check. It relies on #2520 landing first (and I will reference the text assuming that lands).

Currently the definition of "discard a Document" has a funny note at the bottom of its six-step algorithm:

Whenever a Document object is discarded, it is also removed from the owner set of each worker whose set contains that Document.

Indeed, in the section "The worker's lifetime," we have

Whenever a Document object is discarded, it must be removed from the owner set of each WorkerGlobalScope object whose set contains that Document object.

This seems very strange. We should just move that latter normative statement into the algorithm for discarding a document, and get rid of the non-normative note.

[annevk]

This seems like a good idea. I suspect it was this way to enable publishing workers as a distinct document, but even if we ever decided to do that again, we would still want it to be tightly coupled as you suggest.

[donovanglover]

I found the two sections mentioned above and the algorithm for discarding a document. Just to clarify, I have to make a list item for the latter statement and get rid of the old <p class="note">?

[domenic]

Yeah, that plus remove the paragraph in "The worker's lifetime" section, since now it's centralized.