Remove mention of percentage in decoration-trim (#12597)

The grammar for text-decoration-trim does not accept percentages, so remove (at least for now) any mention of how percentages are resolved for this property.

Author: jfkthame

css-text-decor-4/Overview.bs

@@ -902,7 +902,7 @@ Text Decoration Line Trimming and Extension: the 'text-decoration-trim' property
 		and the [=end=] edge of the last fragment,
 		and may accumulate to other fragments if the amount of the trim
 		is more than the length of the fragment.
-		Percentages are relative to the total length of the [=decorating box=].
+		<!-- Percentages are relative to the total length of the [=decorating box=]. -->
 	* for ''box-decoration-break/clone''
 		trimming is applied to each fragment independently.
 		<!-- and percentages are relative to the length of that fragment individually -->
@@ -2210,4 +2210,4 @@ No new privacy considerations have been reported on this specification.
 
 <h2 class=no-num id=security>Security Considerations</h2>
 
-No new security considerations have been reported on this specification.
+No new security considerations have been reported on this specification.