Update user study MP4 location

I turned off public access to the s3 bucket. See raft-dev discussion
<https://groups.google.com/g/raft-dev/c/y23gsXlo_SM>.

Author: ongardie

index.html

@@ -605,7 +605,7 @@ <h2>Talks</h2>
         <td>Video (screencast)</td>
         <td>
           <a href="https://youtu.be/YbZ3zDzDnrw">YouTube</a>
-          <a href="https://raftuserstudy.s3-us-west-1.amazonaws.com/raft.mp4">MP4</a>
+          <a href="https://ongardie.net/static/raft/userstudy/raft.mp4">MP4</a>
         </td>
       </tr>
       <tr>