[css-conditional-3] Remove procedure to set readonly CSSMediaRule.con… (w3c#8796)

Author: cdoublev

css-conditional-3/Overview.bs

@@ -812,10 +812,6 @@ js/CSSConditionRule.html
   <dd>The <code>conditionText</code> attribute (defined on the <code>CSSConditionRule</code> parent rule),
     on getting, must return the value of <code>media.mediaText</code> on the rule.
     <wpt title="Value of CSSMediaRule.conditionText matches value of media.mediaText."></wpt>
-
-    Setting the <code>conditionText</code> attribute
-      must set the <code>media.mediaText</code> attribute on the rule.
-    <wpt title="Setting CSSMediaRule.conditionText also sets .media.mediaText."></wpt>
 </dl>