Editorial: remove a no-op from the Response constructor

Found in #479.

Author: annevk

fetch.bs

@@ -5096,19 +5096,9 @@ constructor, when invoked, must run these steps:
  <a for=response>status message</a> to
  <var>init</var>'s <code>statusText</code> member.
 
- <li>
-  <p>If <var>init</var>'s <code>headers</code> member is present, run these
-  substeps:
-
-  <ol>
-   <li><p>Empty <var>r</var>'s
-   <a for=Response>response</a>'s
-   <a for=response>header list</a>.
-
-   <li><p><a lt=fill for=Headers>Fill</a> <var>r</var>'s
-   {{Headers}} object with <var>init</var>'s <code>headers</code>
-   member. Rethrow any exceptions.
-  </ol>
+ <li><p>If <var>init</var>'s <code>headers</code> member is present, then <a for=Headers>fill</a>
+ <var>r</var>'s {{Headers}} object with <var>init</var>'s <code>headers</code> member. Rethrow any
+ exceptions.
 
  <li>
   <p>If <var>body</var> is non-null, run these substeps: