[css-text-4] Align the language matching logic with selectors

I suspect selectors will eventually do canonicalization, but that isn't
a settled question, and until then, being consistent is more important.

Author: frivoal

css-text-4/Overview.bs

@@ -200,8 +200,6 @@ Detecting Word Boundaries: the 'word-boundary-detection' property</h4>
 			in an extended filtering operation
 			per [[RFC4647]] <cite>Matching of Language Tags</cite> (section 3.3.2)
 			with both the [=content language=] and <<lang>>
-			<i>canonicalized</i> and converted to <i>extlang form</i>
-			as per section 4.5 of [[!RFC5646]],
 			then the [=used value=] is ''word-boundary-detection/normal'',
 			and this property has no effect on this element.
 			Otherwise,