[css-values] Use the official Issue Tracking metadata.

Author: tabatkins

css-values/Overview.bs

@@ -19,7 +19,7 @@ Editor: Tab Atkins, Google, http://xanthir.com/contact/
 Editor: fantasai, http://fantasai.inkedblade.net/contact
 Former Editor: Håkon Wium Lie, Opera Software, howcome@opera.com
 Abstract: This CSS3 module describes the common values and units that CSS properties accept and the syntax used for describing them in CSS property definitions.
-!Issue Tracking: <a rel="issues" href="http://www.w3.org/Style/CSS/Tracker/products/33">http://www.w3.org/Style/CSS/Tracker/products/33</a>
+Issue Tracking: Tracker http://www.w3.org/Style/CSS/Tracker/products/33
 At Risk: ''calc()'', ''toggle()'', ''attr()''
 Ignored Terms: <spacing-limit>, containing block
 </pre>