Remove Azure SQL Edge Wind Turbine Demo

Azure SQL Edge was retired on September 30, 2025, making the Wind Turbine Demo
project obsolete. This commit removes:

- Complete Wind Turbine Demo project (125 files)
- IoT Edge sensor modules and configurations
- React web application with package-lock.json (originally by Vasiya Krishnan)
- Machine learning models and training scripts
- ARM templates and deployment scripts

The readme.md has been updated to:
- Explain the retirement of Azure SQL Edge
- Provide links to archived documentation
- Suggest alternative solutions for edge database scenarios

For historical reference, see:
https://learn.microsoft.com/en-us/previous-versions/azure/azure-sql-edge/

Retirement announcement:
https://azure.microsoft.com/updates/v2/azure-sql-edge-retirement

Author: MikeRayMSFT