DNR: Remove mention of addDynamicRules from docs.

addDynamicRules method was recently removed in r714353 and replaced with
updateDynamicRule. Remove the last mention of addDynamicRules from the docs.

BUG=1023501

Change-Id: Ia00669bc84fbb0136a9f2cfe73d37b474e3579bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1918519Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Reviewed-by: Kelvin Jiang <kelvinjiang@chromium.org>
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715505}

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

@@ -156,9 +156,9 @@ extension can add is bound by the
 <h2 id="dynamic-rules">Dynamic rules</h2>
 
 <p>
-To add rules dynamically, extensions can use the
-<a href="#method-addDynamicRules">
-chrome.declarativeNetRequest.addDynamicRules</a> API method.
+To add or remove rules dynamically, extensions can use the
+<a href="#method-updateDynamicRules">
+chrome.declarativeNetRequest.updateDynamicRules</a> API method.
 
 <ul>
 <li>