Convert a function from Promises to async/await

This is a small readability improvement, but mostly a canary to test
that the async-await support added in the previous commit is working.

src/sidebar/services/oauth-auth.js

@@ -281,15 +281,14 @@ function auth(
    *
    * This revokes and then forgets any OAuth credentials that the user has.
    */
-  function logout() {
-    return Promise.all([tokenInfoPromise, oauthClient()])
-      .then(([token, client]) => {
-        return client.revokeToken(token.accessToken);
-      })
-      .then(() => {
+  async function logout() {
+    const [token, client] = await Promise.all([
+      tokenInfoPromise,
+      oauthClient(),
+    ]);
+    await client.revokeToken(token.accessToken);
     tokenInfoPromise = Promise.resolve(null);
     localStorage.removeItem(storageKey());
-      });
   }
 
   listenForTokenStorageEvents();