Remove git submodules (x402 and modelcontextprotocol)

Remove x402 and modelcontextprotocol submodules as they are not needed.
The project uses npm packages instead:
- x402@^0.6.5 from npm registry
- @modelcontextprotocol/sdk@^1.0.4 from npm registry

Removed:
- x402/ submodule directory
- modelcontextprotocol/ submodule directory
- .gitmodules configuration file

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

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

Author: wtfsayo