VideoJS: don't use videojs.registerPlugin() to start Google Analytics

The `registerPlugin()` call should only be done once, and not for every
video shown.

This removes the warning about the 'analytics' plugin already being
registered, which you see when navigating from one video to another via
the JSTree.

src/templates/nodes/custom/asset/video/view_embed.pug

@@ -59,16 +59,14 @@ script(type="text/javascript").
 		}
 	};
 
-	videojs.registerPlugin('analytics', function() {
+	videojs(videoPlayer, options).ready(function() {
 		this.ga({
 			'eventLabel' : '{{ node._id }} - {{ node.name }}',
 			'eventCategory' : '{{ node.project }}',
 			'eventsToTrack' : ['start', 'error', 'percentsPlayed']
 		});
-	});
-
-	videojs(videoPlayer, options).ready(function() {
 		this.hotkeys();
+
 	});
 
 	function addVideoPlayerButton(data) {