docs(readme): remove grpcurl walkthrough #4584

User Story

I need the top-level OpenShell README to omit the “Test the gRPC API with grpcurl” walkthrough.

Description

Remove the “Test the gRPC API with grpcurl” heading and its entire walkthrough from README.md.

Context

The section was added in #3161 alongside gRPC server reflection. This task concerns README content only; it does not change the gateway or reflection support.

Definition of Done

• README.md no longer contains the “Test the gRPC API with grpcurl” section or its example commands.
• The surrounding README sections remain intact.