Remove broken debug depth options in Scene.js

[ebogo1]

This PR removes some code that's been broken for a while: #6763. If we ever fix this code these commits can be reverted, but for now it's helpful to simplify Scene.js, GlobeDepth.js, and PickDepth.js so the Framebuffer code can be refactored.

• Removes debugGlobeDepthViewportCommand in GlobeDepth
• Removes debugPickDepthViewportCommand in PickDepth
• Removes debugShowGlobeDepth and debugShowPickDepth (which was only set through the inspector) options from Scene
• Removes debugGlobeDepths array in View
• Removes globe depth and pick depth toggles in the CesiumInspector widget and view model
• Removes a test testing debug globe depth in SceneSpec

[cesium-concierge]

Thanks for the pull request @ebogo1!

• ✔️ Signed CLA found.
• ❔ CHANGES.md was not updated.
  • If this change updates the public API in any way, please add a bullet point to CHANGES.md.

Reviewers, don't forget to make sure that:

• Cesium Viewer works.
• Works in 2D/CV.

[lilleyse]

Since this property is part of the public API removing it counts as a breaking change and should be mentioned in CHANGES.md. I don't think we need a deprecation period since it is for debugging only and has been broken for a while now.

[lilleyse]

Same comment about mentioning both of these in the breaking changes section.

[ebogo1]

@lilleyse I made the changes above. Should the CHANGES.md entry have any more info? The original issue says the debug depths may have been broken since 1.45, but usually any extra info in the Breaking section is for alternative APIs to use after deprecation.

[lilleyse]

That should be fine. Thanks @ebogo1.