function removeExtensionsUsed(gltf, extension) {
  const extensionsUsed = gltf.extensionsUsed;
  if (defined(extensionsUsed)) {
    const index = extensionsUsed.indexOf(extension);
    if (index >= 0) {
      extensionsUsed.splice(index, 1);
    }
    removeExtensionsRequired(gltf, extension);
    if (extensionsUsed.length === 0) {
      delete gltf.extensionsUsed;
    }
  }
}
Removes an extension from gltf.extensionsUsed and gltf.extensionsRequired if it is present.

@param {object} gltf A javascript object containing a glTF asset.
@param {string} extension The extension to remove.

@private