ref(tests): remove XMLHttpRequest in mock API (#102986)

this isn't needed as all tests pass without it, but it breaks the msw
poc because the service worker intercepts that "request" too

Author: TkDodo

static/app/__mocks__/api.tsx

@@ -275,8 +275,7 @@ class Client implements ApiNamespace.Client {
             abort: () => {},
             then: () => {},
             error: () => {},
-          },
-          new XMLHttpRequest()
+          }
         );
 
         this.handleRequestError(