chore: remove Firefox CORS workaround

See angular#1468

src/ng/httpBackend.js

@@ -66,26 +66,6 @@ function createHttpBackend($browser, XHR, $browserDefer, callbacks, rawDocument,
         if (xhr.readyState == 4) {
           var responseHeaders = xhr.getAllResponseHeaders();
 
-          // TODO(vojta): remove once Firefox 21 gets released.
-          // begin: workaround to overcome Firefox CORS http response headers bug
-          // https://bugzilla.mozilla.org/show_bug.cgi?id=608735
-          // Firefox already patched in nightly. Should land in Firefox 21.
-
-          // CORS "simple response headers" http://www.w3.org/TR/cors/
-          var value,
-              simpleHeaders = ["Cache-Control", "Content-Language", "Content-Type",
-                                  "Expires", "Last-Modified", "Pragma"];
-          if (!responseHeaders) {
-            responseHeaders = "";
-            forEach(simpleHeaders, function (header) {
-              var value = xhr.getResponseHeader(header);
-              if (value) {
-                  responseHeaders += header + ": " + value + "\n";
-              }
-            });
-          }
-          // end of the workaround.
-
           // responseText is the old-school way of retrieving response (supported by IE8 & 9)
           // response and responseType properties were introduced in XHR Level2 spec (supported by IE10)
           completeRequest(callback,

test/ng/httpBackendSpec.js

@@ -190,9 +190,6 @@ describe('$httpBackend', function() {
       };
 
       this.getAllResponseHeaders = valueFn('');
-      // for temporary Firefox CORS workaround
-      // see https://github.com/angular/angular.js/issues/1468
-      this.getResponseHeader = valueFn('');
     }
 
     callback.andCallFake(function(status, response) {