message: Simplify boombox example
diff: <input name="scale" type="float" value="1.0" />
  <input name="space" type="string" value="tangent" />
  </normalmap>
  - <extract name="extract_occlusion" type="float">
  - <input name="in" type="vector3" nodename="image_orm" />
  - <input name="index" type="integer" value="0" />
  - </extract>
  - <extract name="extract_roughness" type="float">
  - <input name="in" type="vector3" nodename="image_orm" />
  - <input name="index" type="integer" value="1" />
  - </extract>
  - <extract name="extract_metallic" type="float">
  - <input name="in" type="vector3" nodename="image_orm" />
  - <input name="index" type="integer" value="2" />
  - </extract>
  <output name="out_basecolor" type="color3" nodename="image_basecolor" />
  <output name="out_emission" type="color3" nodename="image_emission" />
  <output name="out_normal" type="vector3" nodename="normalmap" />
  - <output name="out_occlusion" type="float" nodename="extract_occlusion" />
  - <output name="out_roughness" type="float" nodename="extract_roughness" />
  - <output name="out_metallic" type="float" nodename="extract_metallic" />
  + <output name="out_orm" type="vector3" nodename="image_orm" />
  </nodegraph>
  <gltf_pbr name="SR_boombox" type="surfaceshader">
  <input name="base_color" type="color3" nodegraph="NG_boombox" output="out_basecolor" />
  - <input name="metallic" type="float" nodegraph="NG_boombox" output="out_metallic" />
  - <input name="roughness" type="float" nodegraph="NG_boombox" output="out_roughness" />
  + <input name="metallic" type="float" nodegraph="NG_boombox" output="out_orm" channels="z" />
  + <input name="roughness" type="float" nodegraph="NG_boombox" output="out_orm" channels="y"/>
  <input name="normal" type="vector3" nodegraph="NG_boombox" output="out_normal" />
  - <input name="occlusion" type="float" nodegraph="NG_boombox" output="out_occlusion" />
  + <input name="occlusion" type="float" nodegraph="NG_boombox" output="out_orm" channels="x"/>
  <input name="transmission" type="float" value="0" />
  <input name="ior" type="float" value="1.5" />
  <input name="specular" type="float" value="1" />
  