Event: remove guard for falsy handler argument of jQuery#on method

(cherry-picked from fac67a984268ef8f7de952666fda6d8d32754f5f)

Since we don't have this in off method and its a common perception
that this is a rudiment code

Ref gh-2248
Closes gh-2249

src/event.js

@@ -1002,8 +1002,6 @@ jQuery.fn.extend({
 		}
 		if ( fn === false ) {
 			fn = returnFalse;
-		} else if ( !fn ) {
-			return this;
 		}
 
 		if ( one === 1 ) {

test/unit/event.js

@@ -5,20 +5,6 @@ module( "event", {
 	teardown: moduleTeardown
 });
 
-test("null or undefined handler", function() {
-	expect(2);
-	// Supports Fixes bug #7229
-	try {
-		jQuery("#firstp").on( "click", null );
-		ok(true, "Passing a null handler will not throw an exception");
-	} catch ( e ) {}
-
-	try {
-		jQuery("#firstp").on( "click", undefined );
-		ok(true, "Passing an undefined handler will not throw an exception");
-	} catch ( e ) {}
-});
-
 test("on() with non-null,defined data", function() {
 
 	expect(2);