Use a single exception for name validation (follow up)

This addresses two cases overlooked by 61f40b0:

* The QName production is a strict subset of the Name production.  To
  avoid confusion, drop "or Name" from the definition of "validate
  a qualifiedName".

* The non-normative "for web developers" text for `createElementNS`
  was not updated by the original commit.

Fixes: whatwg#671

dom.bs

@@ -249,7 +249,7 @@ added.
 
 <p>To <dfn export>validate</dfn> a <var>qualifiedName</var>, <a>throw</a> an
 "{{InvalidCharacterError!!exception}}" {{DOMException}} if <var>qualifiedName</var> does not match
-the <code><a type>Name</a></code> or <code><a type>QName</a></code> production.
+the <code><a type>QName</a></code> production.
 
 To <dfn export>validate and extract</dfn> a <var>namespace</var> and <var>qualifiedName</var>,
 run these steps:
@@ -5021,15 +5021,13 @@ for the <a>context object</a>.
   <var>qualifiedName</var> or null. Its <a for=Element>local name</a> will be everything after
   "<code>:</code>" (U+003E) in <var>qualifiedName</var> or <var>qualifiedName</var>.
 
-  <p>If <var>localName</var> does not match the <code><a type>Name</a></code> production an
+  <p>If <var>qualifiedName</var> does not match the <code><a type>QName</a></code> production an
   "{{InvalidCharacterError!!exception}}" {{DOMException}} will be thrown.
 
   <p>If one of the following conditions is true a "{{NamespaceError!!exception}}" {{DOMException}}
   will be thrown:
 
   <ul>
-   <li><var>localName</var> does not match the
-   <code><a type>QName</a></code> production.
    <li><a for=Element>Namespace prefix</a>
    is not null and <var>namespace</var> is the empty string.
    <li><a for=Element>Namespace prefix</a>