watch.html: Move loose inline javascript into watch.js

The number of inline code blocks and the dependencies between them
became unmanageable.

From 9d96c07a3c2e68f1893634574c3be64e41a2c041 Mon Sep 17 00:00:00 2001
From: James Taylor <user234683@users.noreply.github.com>

youtube/static/js/av-merge.js

@@ -19,13 +19,6 @@
 
 // TODO: Call abort to cancel in-progress appends?
 
-
-var avMerge;
-
-function avInitialize(...args){
-    avMerge = new AVMerge(...args);
-}
-
 function AVMerge(video, srcPair, startTime){
     this.videoSource = srcPair[0];
     this.audioSource = srcPair[1];