[cssom] (editorial) bikeshed fixes with dom xrefs

Author: zcorpan

cssom/Overview.bs

@@ -110,7 +110,6 @@ urlPrefix: https://fetch.spec.whatwg.org/#
 </pre>
 
 <pre class='link-defaults'>
-spec: dom-core-ls; type: interface; text: Document
 spec:css-display-3; type:value; for:display; text:table
 spec:css-color-4; type:property; text:color
 spec:css-position-3; type:property; text:left