Core: simplify "each" stylesheet iteration test

(cherry-picked from fcb6c4d1d6552c7e54df16a36b171858bdf0553f)
Closes gh-2089

test/unit/core.js

@@ -1183,7 +1183,7 @@ test("jQuery.each(Object,Function)", function() {
 	jQuery.each( document.styleSheets, function() {
 		i++;
 	});
-	equal( i, 2, "Iteration over document.styleSheets" );
+	equal( i, document.styleSheets.length, "Iteration over document.styleSheets" );
 });
 
 test("jQuery.makeArray", function(){