Remove ie8/9 special CORS treatment and btoa polyfill

lib/adapters/xhr.js

@@ -6,7 +6,6 @@ var buildURL = require('./../helpers/buildURL');
 var parseHeaders = require('./../helpers/parseHeaders');
 var isURLSameOrigin = require('./../helpers/isURLSameOrigin');
 var createError = require('../core/createError');
-var btoa = (typeof window !== 'undefined' && window.btoa && window.btoa.bind(window)) || require('./../helpers/btoa');
 
 module.exports = function xhrAdapter(config) {
   return new Promise(function dispatchXhrRequest(resolve, reject) {
@@ -18,22 +17,6 @@ module.exports = function xhrAdapter(config) {
     }
 
     var request = new XMLHttpRequest();
-    var loadEvent = 'onreadystatechange';
-    var xDomain = false;
-
-    // For IE 8/9 CORS support
-    // Only supports POST and GET calls and doesn't returns the response headers.
-    // DON'T do this for testing b/c XMLHttpRequest is mocked, not XDomainRequest.
-    if (process.env.NODE_ENV !== 'test' &&
-        typeof window !== 'undefined' &&
-        window.XDomainRequest && !('withCredentials' in request) &&
-        !isURLSameOrigin(config.url)) {
-      request = new window.XDomainRequest();
-      loadEvent = 'onload';
-      xDomain = true;
-      request.onprogress = function handleProgress() {};
-      request.ontimeout = function handleTimeout() {};
-    }
 
     // HTTP basic authentication
     if (config.auth) {
@@ -48,8 +31,8 @@ module.exports = function xhrAdapter(config) {
     request.timeout = config.timeout;
 
     // Listen for ready state
-    request[loadEvent] = function handleLoad() {
-      if (!request || (request.readyState !== 4 && !xDomain)) {
+    request.onreadystatechange = function handleLoad() {
+      if (!request || request.readyState !== 4) {
         return;
       }