refactor($http) Simplify code by removing workarounds for older versions of Internet Explorer

This removes a workaround for IE 8 and and error handling for IE6.

Closes #9300

docs/content/error/$httpBackend/noxhr.ngdoc

@@ -1,10 +0,0 @@
-@ngdoc error
-@name $httpBackend:noxhr
-@fullName Unsupported XHR
-@description
-
-This error occurs in browsers that do not support XmlHttpRequest. AngularJS
-supports Safari, Chrome, Firefox, Opera, IE8 and higher, and mobile browsers
-(Android, Chrome Mobile, iOS Safari). To avoid this error, use an officially
-supported browser.
-

src/ng/httpBackend.js

@@ -1,17 +1,7 @@
 'use strict';
 
-function createXhr(method) {
-    //if IE and the method is not RFC2616 compliant, or if XMLHttpRequest
-    //is not available, try getting an ActiveXObject. Otherwise, use XMLHttpRequest
-    //if it is available
-    if (msie <= 8 && (!method.match(/^(get|post|head|put|delete|options)$/i) ||
-      !window.XMLHttpRequest)) {
-      return new window.ActiveXObject("Microsoft.XMLHTTP");
-    } else if (window.XMLHttpRequest) {
-      return new window.XMLHttpRequest();
-    }
-
-    throw minErr('$httpBackend')('noxhr', "This browser does not support XMLHttpRequest.");
+function createXhr() {
+    return new window.XMLHttpRequest();
 }
 
 /**
@@ -59,7 +49,7 @@ function createHttpBackend($browser, createXhr, $browserDefer, callbacks, rawDoc
       });
     } else {
 
-      var xhr = createXhr(method);
+      var xhr = createXhr();
 
       xhr.open(method, url, true);
       forEach(headers, function(value, key) {