Ajax: simplify one ajax call and add explanatory comment

* Remove "async = true" from script transport since it was needed
  for FF < 4 and old Opera which we do not support anymore

* Add comment to "evalUrl" method on why "type" field should be explicit

src/ajax/script.js

@@ -39,7 +39,6 @@ jQuery.ajaxTransport( "script", function( s ) {
 		return {
 			send: function( _, complete ) {
 				script = jQuery("<script>").prop({
-					async: true,
 					charset: s.scriptCharset,
 					src: s.url
 				}).on(

src/manipulation/_evalUrl.js

@@ -5,6 +5,8 @@ define([
 jQuery._evalUrl = function( url ) {
 	return jQuery.ajax({
 		url: url,
+
+		// Make this explicit, since user can override this through ajaxSetup (#11264)
 		type: "GET",
 		dataType: "script",
 		cache: true,