Remove northamerica-northeast1 from Vertex AI regions

... because it does not support long context (> 32K).
https://cloud.google.com/vertex-ai/generative-ai/docs/learn/locations#canada_1

USAGE.md

@@ -44,7 +44,7 @@ gcloud auth application-default set-quota-project <your-project>
 You'll also need to specify the GCP projects and locations where you have Vertex AI quota (comma delimited):
 ```bash
 export CLOUD_ML_PROJECT_ID=<gcp-project-id>
-export VERTEX_AI_LOCATIONS=us-west1,us-west4,us-east4,us-central1,northamerica-northeast1
+export VERTEX_AI_LOCATIONS=us-west1,us-west4,us-east4,us-central1
 ```
 
 #### OpenAI