undo CL 11967047 / d44f1df51f4d

rethinking about this

««« original CL description
go.talks: add support for mouse wheel interaction on the slides.

R=adg
CC=golang-dev
https://golang.org/cl/11967047
»»»

R=adg, r
CC=golang-dev
https://golang.org/cl/12217043
diff --git a/present/static/slides.js b/present/static/slides.js
index 5bbf5e8..863e7ac 100644
--- a/present/static/slides.js
+++ b/present/static/slides.js
@@ -297,14 +297,6 @@
   document.body.removeEventListener('touchend', handleTouchEnd, true);  
 };
 
-/* Mouse wheel events */
-
-function handleMouseWheel(event) {
-  var delta = event.wheelDelta;
-  if (delta > 0) nextSlide();
-  if (delta < 0) prevSlide();
-}
-
 /* Preloading frames */
 
 function disableSlideFrames(no) {
@@ -373,10 +365,6 @@
   /* Swiping */
   
   document.body.addEventListener('touchstart', handleTouchStart, false);
-
-  /* Scrolling */
-
-  document.body.addEventListener('mousewheel', handleMouseWheel, false);
 }
 
 /* Hash functions */