Clarify example on example with media before signaling

As per discussion in #1708:
* Change the title to 'with incoming media before signaling'
* Change the intro to add 'This code shows the receiving side'
* Remove the 'selfView' code

close #1708

webrtc.html

@@ -11810,11 +11810,11 @@ <h3>Advanced Peer-to-peer Example with Warm-up</h3>
       </div>
     </section>
     <section>
-      <h3>Peer-to-peer Example with media before signaling</h3>
+      <h3>Peer-to-peer Example with incoming media before signaling</h3>
       <div>
         <p>The answerer may wish to send media in parallel with sending the
         answer, and the offerer may wish to render the media before the answer
-        arrives.</p>
+        arrives. This code shows the receiving side.</p>
         <pre class="example highlight">
 const signaling = new SignalingChannel();
 const configuration = {iceServers: [{urls: 'stuns:stun.example.org'}]};
@@ -11839,16 +11839,6 @@ <h3>Peer-to-peer Example with media before signaling</h3>
       console.error(err);
     }
   };
-
-  try {
-    // get a local stream, show it in a self-view and add it to be sent
-    const stream = await navigator.mediaDevices.getUserMedia({audio: true, video: true});
-    selfView.srcObject = stream;
-    // Render the media even before ontrack fires.
-    remoteView.srcObject = new MediaStream(pc.getReceivers().map((r) =&gt; r.track));
-  } catch (err) {
-    console.error(err);
-  }
 };
 
 signaling.onmessage = async (event) =&gt; {