[css-2015] Use dbaron's wording for the licensing clause.

Author: fantasai

css-2015/Overview.bs

@@ -465,11 +465,12 @@ Requirements for Responsible Implementation of CSS</h2>
 				as they get ironed out through the standards/bugfixing process.
 			</details>
 
-			<p>Vendors <em>should</em> provide spec-editing and testing resources
-			to complete standardization of such features.
-			<ins>Vendors <em>should not</em> use this clause as an excuse to release features
-			that cannot be freely implemented by their competitors
-			(due to platform dependency, licensing restrictions, etc.).</ins>
+			<p>Vendors should <ins>make it possible for other implementors
+			to freely implement any features that they do ship.
+			To this end, they should</ins> provide spec-editing and testing resources
+			to complete standardization of such features,
+			<ins>and avoid other obstacles (e.g., platform dependency, licensing restrictions)
+			to their competitors shipping the feature.</ins>
 
 		<h4 id="proprietary">
 		Proprietary and Non-standardized Features</h4>