Remove monkeypatch of globalThis.self in ShadowRealm

As per whatwg/html#9893, ShadowRealmGlobalScope
should have a `self` attribute already. There is no need to monkeypatch it
for the test harness.

resources/idlharness-shadowrealm.js

@@ -23,9 +23,6 @@ function fetch_text(url) {
 function idl_test_shadowrealm(srcs, deps) {
     promise_setup(async t => {
         const realm = new ShadowRealm();
-        // https://github.com/web-platform-tests/wpt/issues/31996
-        realm.evaluate("globalThis.self = globalThis; undefined;");
-
         realm.evaluate(`
             globalThis.self.GLOBAL = {
                 isWindow: function() { return false; },

tools/serve/serve.py

@@ -438,7 +438,6 @@ class ShadowRealmInWindowHandler(HtmlWrapperHandler):
 <script>
 (async function() {
   const r = new ShadowRealm();
-  r.evaluate("globalThis.self = globalThis; undefined;");
   r.evaluate(`func => {
     globalThis.fetch_json = (resource) => {
       const thenMethod = func(resource);