Cleaning up React + Apollo example

- Simplify test
- Fix bug in makeApolloClient (pageProps was missing)
- Add comment about having to instantiate a new Apollo Client per request
- Remove _error.page.jsx
- Use static page title
- Remove unnecessary package.json scripts (and the packages for them)

examples/react-apollo/.test.spec.js

@@ -0,0 +1,10 @@
+const { fetchHtml, run } = require("../../tests/setup");
+
+run("npm run start");
+
+test("page content is rendered to HTML", async () => {
+  const html = await fetchHtml("/");
+  expect(html).toContain("<h1>Welcome to <code>vite-plugin-ssr</code></h1>");
+  expect(html).toContain("<li>Angola</li><li>Antarctica</li><li>Argentina</li><li>American Samoa</li>");
+  expect(html).toContain("pageProps: (function(a){return {initialApolloState:{ROOT_QUERY:");
+});