CSS: Don't expose jQuery.swap

jQuery.swap was an undocumented API used only internally. With the modular
AMD system we currently have it's not necessary to expose this function
publicly under the jQuery object.

Fixes gh-2058
Closes gh-2182

src/css/var/swap.js

@@ -1,9 +1,7 @@
-define([
-	"../core"
-], function( jQuery ) {
+define(function() {
 
 // A method for quickly swapping in/out CSS properties to get correct calculations.
-jQuery.swap = function( elem, options, callback, args ) {
+return function swap( elem, options, callback, args ) {
 	var ret, name,
 		old = {};
 
@@ -23,6 +21,4 @@ jQuery.swap = function( elem, options, callback, args ) {
 	return ret;
 };
 
-return jQuery.swap;
-
 });