Remove canCollapseAnonymousBlockChild.

The only place it's used now is making it so that
anonymous flex items don't do ellipsizing the same
way anonymous items inside a block would. This
is something we don't need, especially now that
we only have anonymous paragraphs around text nodes.

It's not clear to me if we want this looking at the
parent behavior at all, but that's something that
can be fixed in a followup.

Also delete some dead anonymous block functions.

R=esprehn@chromium.org

Review URL: https://codereview.chromium.org/741893002