[css-content] content: contents will not be compatible. #4632

I was fixing a Gecko compat issue (webcompat/web-bugs#46914) which is present because we always serialize content: normal as content: none, even on elements.

I'm going to fix Gecko to follow the spec and getComputedStyle() returns none for pseudo-elements, but not for elements. But such code wouldn't work if we were to make content: normal compute to content: contents on elements either, which is what the latest draft specifies: https://drafts.csswg.org/css-content/#content-property

So I propose for content: normal to compute to itself for elements, and removing content: contents from the spec.