docs: Removed extraneous "system components" info

The "system components" section contained some info left over from
Preview 1's "system apps" section. Per clarification from Ben, I've
removed it.

Also added link to Ben's I/O video.

See first comment for doc stage location.

Change-Id: I1efb11ffe69880893209a64b282f2616fe7d9f22

docs/html/preview/features/runtime-permissions.jd

@@ -35,12 +35,23 @@ page.image=images/permissions_check.png
 <!--
   <h2>See also</h2>
   <ol>
-    <li></li>
+    <li>
+    </li>
   </ol>
 -->
+
   </div> <!-- qv -->
 </div> <!-- qv-wrapper -->
 
+<!-- video box -->
+<a class="notice-developers-video"
+    href="https://www.youtube.com/watch?v=f17qe9vZ8RM">
+<div>
+    <h3>Video</h3>
+    <p>Google I/O 2015—Android M Permissions: Best Practices for
+      Developers</p>
+</div>
+</a>
 
 <p>
   The M Developer Preview introduces a new app permissions model which
@@ -204,12 +215,7 @@ page.image=images/permissions_check.png
 
 <ul>
   <li>System components automatically receive all
-  the permissions listed in their manifests. However, the user can still revoke
-  permissions at any time by going to the system's <strong>Settings</strong>
-  app and choosing <strong>Apps &gt;</strong> <i>app_name</i> <strong>&gt;
-  Permissions</strong>. Because users can revoke these permissions at will,
-  the app should continue to check for permissions at run
-  time and request them if necessary.
+  the permissions listed in their manifests.
   </li>
 
   <li>If the app requests permissions in the manifest that fall under {@link