Rogue Triangle on SheenChair

[Tim]

An odd triangle seems to be showing up when loading SheenChair using https://github.khronos.org/glTF-Sample-Viewer-Release/ with the default settings, Mango or Peacock chair. Others have reported that they cannot see the extra triangle in the Sheen Chair when loading the model from Sample-Assets (see https://github.com/KhronosGroup/glTF-Sample-Assets/blob/main/Models.md

[Ed Mackey]

This was introduced with #470.

[Patrick Härtl]

Fixed for now by reverting #470