Editorial: update custom element cross-spec references

dom.bs

@@ -96,19 +96,6 @@ urlPrefix: https://slightlyoff.github.io/ServiceWorker/spec/service_worker/#
         text: service worker
         text: script resource
         text: has ever been evaluated flag
-urlPrefix: https://rawgit.com/w3c/webcomponents/15a203c8393aef0df7223ab1d43406aa11a7e71e/spec/custom/index.html#
-    type: selector; url: dfn-defined; text: :defined
-    type: dfn; urlPrefix: dfn-
-        text: look up a custom element definition; url: look-up-custom-element-definition
-        text: type extension
-        text: name; url: element-definition-name; for: custom element definition
-        text: local name; url: element-definition-local-name; for: custom element definition
-        text: constructor; url: element-definition-constructor; for: custom element definition
-        text: upgrade an element; url: upgrade-a-custom-element
-        text: enqueue a custom element upgrade reaction; url: enqueue-upgrade
-        text: enqueue a custom element callback reaction; url: enqueue-lifecycle-callback
-        text: valid custom element name
-        text: try to upgrade an element; url: try-upgrade
 urlPrefix: https://tc39.github.io/ecma262/#; spec: ECMASCRIPT
     text: Construct; url: sec-construct; type: abstract-op
     text: TypeError; url: sec-native-error-types-used-in-this-standard-typeerror; type: exception
@@ -4756,7 +4743,7 @@ for the <a>context object</a>.
   exception will be thrown.
 
   When supplied, <var>options</var>' <code>is</code> member can be used to create a
-  <a>type extension</a>.
+  <a>customized built-in element</a>.
 
 
  <dt><code><var>element</var> = <var>document</var> . <a method lt=createElementNS()>createElementNS(namespace, qualifiedName [, options])</a></code>
@@ -4800,7 +4787,7 @@ for the <a>context object</a>.
   </ul>
 
   When supplied, <var>options</var>' <code>is</code> member can be used to create a
-  <a>type extension</a>.
+  <a>customized built-in element</a>.
 
  <dt><code><var>documentFragment</var> = <var>document</var> . {{createDocumentFragment()}}</code>
  <dd>Returns a {{DocumentFragment}}
@@ -5620,7 +5607,7 @@ given a <var>document</var>, <var>localName</var>, <var>prefix</var>, <var>names
   <p>If <var>definition</var> is non-null, and <var>definition</var>'s
   <a for="custom element definition">name</a> is not equal to its
   <a for="custom element definition">local name</a> (i.e., <var>definition</var> represents a
-  <a>type extension</a>), then:
+  <a>customized built-in element</a>), then:
 
   <ol>
    <li><p>Let <var>interface</var> be the <a>element interface</a> for <var>localName</var> and the