feat: move FastMCP example to auth0-ai-samples repository

Remove example-fastmcp-mcp from this repository as it has been moved to the
auth0-ai-samples repository for better visibility and discoverability.

New location: https://github.com/auth0-samples/auth0-ai-samples/tree/main/auth-for-mcp/fastmcp-mcp-python

This consolidates Auth0 AI/MCP examples in a dedicated samples repository
alongside other AI integration examples.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: btiernay