DNR: Remove references to removeHeaders in docs.

The removeHeaders action has been removed from the API.

BUG=1085326

Change-Id: I533c885d92373ce8fd888a059f8ded0a9acc6337
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2220831
Auto-Submit: Karan Bhatia <karandeepb@chromium.org>
Commit-Queue: Kelvin Jiang <kelvinjiang@chromium.org>
Reviewed-by: Kelvin Jiang <kelvinjiang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#773868}

chrome/common/extensions/docs/templates/intros/declarativeNetRequest.html

@@ -244,13 +244,6 @@ following order of decreasing precedence:
   <li><code>redirect</code></li>
 </ul>
 
-<p>
-If the request was not blocked or redirected, <code>removeHeaders</code> rules
-are evaluated on the request and response headers. All matching
-<code>removeHeaders</code> rules from extensions that did not have a matching
-<code>allow</code> or <code>allowAllRequests</code> action are evaluated.
-</p>
-
 <h3 id="web-request-comparison">
   Comparison with the <a href="webRequest">webRequest</a> API
 </h3>