Uncomment OpenCV 4.5.4 requirement in detect.py

[jebastin-nadar]

pip package of opencv-python has been updated to version 4.5.4. https://pypi.org/project/opencv-python/
requirement can now be uncommented.

related #4811 (comment)

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Improvement in ONNX model support with environment checks within the detect.py script.

📊 Key Changes

• Uncommented requirement check for OpenCV when using ONNX models with DNN.

🎯 Purpose & Impact

• Purpose: Ensures that users have the correct version of OpenCV installed when opting to run the model with OpenCV's DNN module.
• Impact: Enhances user experience by providing clear requirements, potentially reducing setup issues and improving model compatibility. 🛠️

[glenn-jocher]

@SamFC10 PR is merged. Thank you for your contributions to YOLOv5 🚀 and Vision AI ⭐