[cssom-view] Remove incorrect spec prose "emit the scrollend event"

[zcorpan]

https://w3c.github.io/csswg-drafts/cssom-view/#perform-a-scroll

...then perform a smooth scroll of box to position. Once the position has finished updating, emit the scrollend event. Otherwise, perform an instant scroll of box to position. After an instant scroll emit the scrollend event.

Note:​ In the case the VisualViewport was scrolled, yielding no translation changes in the document, emit the scrollend on the VisualViewport just as the scroll event is emitted for VisualViewport scrolling.

This algorithm shouldn't say to fire scrollend events, as that is done in https://w3c.github.io/csswg-drafts/cssom-view/#scrolling-events

If you want, you can include a note that clarifies where events are fired, without sounding like requirements. (See https://wpc.guide/skills/#building-blocks-of-a-spec)

cc @emilio @dlrobertson @argyleink