Event: Remove the event.which shim

All supported browsers implement this property by themselves. The shim was only
needed for IE <9.

Fixes gh-3235
Closes gh-4765
Ref gh-4755

(cherry picked from commit 1a5fff4)

src/event.js

@@ -17,10 +17,7 @@ define( [
 
 "use strict";
 
-var
- rkeyEvent = /^key/,
- rmouseEvent = /^(?:mouse|pointer|contextmenu|drag|drop)|click/,
- rtypenamespace = /^([^.]*)(?:\.(.+)|)/;
+var rtypenamespace = /^([^.]*)(?:\.(.+)|)/;
 
 function returnTrue() {
  return true;
@@ -749,34 +746,7 @@ jQuery.each( {
  targetTouches: true,
  toElement: true,
  touches: true,
-
- which: function( event ) {
- var button = event.button;
-
- // Add which for key events
- if ( event.which == null && rkeyEvent.test( event.type ) ) {
- return event.charCode != null ? event.charCode : event.keyCode;
- }
-
- // Add which for click: 1 === left; 2 === middle; 3 === right
- if ( !event.which && button !== undefined && rmouseEvent.test( event.type ) ) {
- if ( button & 1 ) {
- return 1;
- }
-
- if ( button & 2 ) {
- return 3;
- }
-
- if ( button & 4 ) {
- return 2;
- }
-
- return 0;
- }
-
- return event.which;
- }
+ which: true
 }, jQuery.event.addProp );
 
 jQuery.each( { focus: "focusin", blur: "focusout" }, function( type, delegateType ) {