Use Env Var directly instead of through GoogleAuth() (#1202)

packages/core/src/code_assist/codeAssist.ts

@@ -4,7 +4,6 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { GoogleAuth, AuthClient } from 'google-auth-library';
 import { ContentGenerator } from '../core/contentGenerator.js';
 import { getOauthClient } from './oauth2.js';
 import { setupUser } from './setup.js';
@@ -13,17 +12,7 @@ import { CodeAssistServer, HttpOptions } from './server.js';
 export async function createCodeAssistContentGenerator(
   httpOptions: HttpOptions,
 ): Promise<ContentGenerator> {
-  const authClient = await getAuthClient();
+  const authClient = await getOauthClient();
   const projectId = await setupUser(authClient);
   return new CodeAssistServer(authClient, projectId, httpOptions);
 }
-
-async function getAuthClient(): Promise<AuthClient> {
-  try {
-    // Try for Application Default Credentials.
-    return await new GoogleAuth().getClient();
-  } catch (_) {
-    // No Application Default Credentials so try Oauth.
-    return await getOauthClient();
-  }
-}