Don't try to pre-populate an octokit

I argue that calling createOctokit(false) adds no benefit. If an
authenticated session already exists then this silently create an
octokit, which makes getOctokit() a no-op just returning the field.
However if there is already an authenticated session then getOctokit()
would already be able to create an octokit without prompting the user.

On the other hand if there isn't an authenticated session then we
won't be able to pre-populate an octokit, so getOctokit() will have
to prompt the user anyway.

Not calling createOctokit(false) in registerListeners also doesn't
change behaviour. If the user is authenticated in the new session then
we would be able to create an octokit instance wihtout prompting in
getOctokit anyway. If the user is not authenticated in the new session
then we won't be able to create an instance without prompting either way.

The only benefit I can think of is that it moves a tiny amount of
computation earlier in the pipeline, but the amount of computation is
tiny and it isn't any more async than it would be if it happened in
getOctokit(). I don't think this is worth making the code more complex.

extensions/ql-vscode/src/authentication.ts

@@ -34,7 +34,6 @@ export class Credentials {
   ): Promise<Credentials> {
     const c = new Credentials();
     c.registerListeners(context);
-    c.octokit = await c.createOctokit(false);
     return c;
   }
 
@@ -76,7 +75,7 @@ export class Credentials {
     context.subscriptions.push(
       vscode.authentication.onDidChangeSessions(async (e) => {
         if (e.provider.id === GITHUB_AUTH_PROVIDER_ID) {
-          this.octokit = await this.createOctokit(false);
+          this.octokit = undefined;
         }
       }),
     );