Revert larger change to setAttributeNs as its no longer neccessary.

Author: lukewarlow

dom.bs

@@ -7329,18 +7329,8 @@ method steps are:
  Trusted Types-compliant attribute value</a> with <var>localName</var>, <var>namespace</var>,
  <var>element</var>, and <var>value</var>. [[!TRUSTED-TYPES]]
 
- <li><p>Let <var>attribute</var> be the result of
- <a lt="get an attribute by namespace and local name">getting an attribute</a> given
- <var>namespace</var>, <var>localName</var>, and <var>element</var>.
-
- <li><p>If <var>attribute</var> is null, create an <a>attribute</a> whose <a for=Attr>namespace</a>
- is <var>namespace</var>, <a for=Attr>namespace prefix</a> is <var>prefix</var>,
- <a for=Attr>local name</a> is <var>localName</var>, <a for=Attr>value</a> is
- <var>verifiedValue</var>, and <a for=Node>node document</a> is <var>element</var>'s
- <a for=Node>node document</a>, then <a lt="append an attribute">append</a> this <a>attribute</a> to
- <var>element</var>, and then return.
-
- <li><p><a lt="change an attribute">Change</a> <var>attribute</var> to <var>verifiedValue</var>.
+ <li><p><a>Set an attribute value</a> for <a>this</a> using <var>localName</var>,
+ <var>verifiedValue</var>, and also <var>prefix</var> and <var>namespace</var>.
 </ol>
 
 <p>The