Delete YOLO class examples

[bomanimc]

Fixes #1145.

Since we no longer support YOLO as a singular modal and have hidden it from our documentation, I think we should also delete the examples.

This PR doesn't delete the ObjectDetector/YOLO implementation, as YOLO can still be used for the ObjectDetector class. That said, I don't have much context on the YOLO deprecation and I'm curious if this something we might want to delete too in a later PR (cc @joeyklee).

[joeyklee]

(Ack! I recently turned off my github email notifications and realized I've missed SO much 🙈 . )

This PR doesn't delete the ObjectDetector/YOLO implementation, as YOLO can still be used for the ObjectDetector class. That said, I don't have much context on the YOLO deprecation and I'm curious if this something we might want to delete too in a later PR

• Yes I think we can remove YOLO from the Object Detector entirely. The way I kind of see it right now, is that we are starting to land on these kind of "high level" model support -- e.g. object detector, face tracking, hand tracking, pose tracking -- and we have some pre-trained model that allows them to run. In ttrying to forefront maintainability, I think it doesn't hurt us to prune things out while we find our bearings amidst such quick growth and all the world happenings, and then work to add things back or build on top of as capacity permits. Does that resonate at all?

[joeyklee]

✅ LGTM -- Before merging, I would just double check with @shiffman to sync up regarding potential coding train videos needing to update references.

[shiffman]

I'm good with this change, I may have referenced YOLO in some tutorials but I can update video descriptions / code examples to use COCOSSD only.