docs: remove Critic agent from built-in agents table (experimental, not ready for course)

Agent-Logs-Url: https://github.com/github/copilot-cli-for-beginners/sessions/19dc97e2-9414-4ddd-8072-fade91ba8516

Co-authored-by: DanWahlin <1767249+DanWahlin@users.noreply.github.com>

Author: Copilot

04-agents-custom-instructions/README.md

@@ -66,7 +66,6 @@ Never used or made an agent? Here's all you need to know to get started for this
 |-------|---------------|--------------|
 | **Plan** | `/plan` or `Shift+Tab` (cycle modes) | Creates step-by-step implementation plans before coding |
 | **Code-review** | `/review` | Reviews staged/unstaged changes with focused, actionable feedback |
-| **Critic** | *Automatic* | Reviews plans and complex implementations using a second model to catch errors early (experimental, Claude models only) |
 | **Init** | `/init` | Generates project configuration files (instructions, agents) |
 | **Explore** | *Automatic* | Used internally when you ask Copilot to explore or analyze the codebase |
 | **Task** | *Automatic* | Executes commands like tests, builds, lints, and dependency installs |