disable for now rgba textures

examples/jsm/exporters/USDZExporter.js

@@ -380,7 +380,6 @@ function buildMaterial( material, textures ) {
             float outputs:r
             float outputs:g
             float outputs:b
-            float outputs:a
             float3 outputs:rgb
         }`;
 
@@ -457,11 +456,6 @@ function buildMaterial( material, textures ) {
 
 		samplers.push( buildTexture( material.alphaMap, 'opacity' ) );
 
-	} else if ( material.map !== null && material.map.format === 1023 ) {
-
-		inputs.push( `${pad}float inputs:opacity.connect = </Materials/Material_${material.id}/Texture_${material.map.id}_diffuse.outputs:a>` );
-		inputs.push( `${pad}float inputs:opacityThreshold = 0.0001` );
-
 	} else {
 
 		inputs.push( `${pad}float inputs:opacity = ${material.opacity}` );