Revert "Allow XHR timeout attribute to be overridden after send(), per spec"

LayoutTests/http/tests/xmlhttprequest/workers/resources/xmlhttprequest-timeout-override-worker.js

-importScripts("worker-pre.js");
-
-function log(message) {
-    postMessage("log " + message);
-}
-
-function done() {
-    postMessage("DONE");
-}
-
-function eventHandler(e) {
-    log(e.type);
-    done();
-}
-
-function init() {
-    try {
-        var xhr = new XMLHttpRequest();
-        xhr.ontimeout = eventHandler;
-        xhr.onabort = eventHandler;
-        xhr.onerror = eventHandler;
-        xhr.onload = eventHandler;
-
-        xhr.timeout = 100000;
-        xhr.open("GET", "../../../resources/load-and-stall.php?name=../resources/test.mp4&stallAt=0&stallFor=1000&mimeType=video/mp4", true);
-
-        // Defer overriding timeout
-        setTimeout(function() {
-            xhr.timeout = 400;
-        }, 200);
-
-        setTimeout(function() {
-            xhr.abort();
-        }, 1000);
-
-        xhr.send();
-    } catch (e) {
-        log(e);
-        done();
-    }
-};