remove mentions of unused [[SourceText]] internal slot; renumber lists

[michaelficarra]

This slot was added by me to the async function proposal, assuming the Function.prototype.toString rewrite would land first. I'm removing these unused internal slot assignments from the main spec text and will be adding them back in #697 once this is merged. In the process, I've renumbered the lists for easier diffing since they were misnumbered to begin with.

[anba]

If this lands before #775, cd1fa44 can be removed in the other PR.

[bterlson]

You guys just love making merge work don't you.

[michaelficarra]

@anba Oh, great! Sorry for the dupe. I hadn't seen your PR.

@bterlson I'm okay just closing this PR as long as cd1fa44 gets in before the ES2017 cutoff. If something else in #775 is going to block it until after the ES2017 cutoff, please just merge this one.

[bterlson]

I am going to review #755 before the cutoff.

@michaelficarra I think the step renumbering can stay and doesn't conflict. Maybe remove only the parts duplicated by cd1fa44?

[anba]

@michaelficarra I think the step renumbering can stay and doesn't conflict. Maybe remove only the parts duplicated by cd1fa44?

It's probably easier to remove cd1fa44 from #755, isn't it? That way we can avoid merge conflicts in either this PR or the other one.

[bterlson]

@anba sure seems fine, I can see @michaelficarra right now which is why I thought to ask him to make this apply cleanly on top of #755 but I can prune cd1fa44.