Remove reference to `diffuse` parameter

`kD` is set to the `color` parameter directly.

examples/js/loaders/MTLLoader.js

@@ -319,7 +319,7 @@ THREE.MTLLoader.MaterialCreator.prototype = {
 
 					// Diffuse color (color under white light) using RGB values
 
-					params[ 'diffuse' ] = new THREE.Color().fromArray( value );
+					params[ 'color' ] = new THREE.Color().fromArray( value );
 
 					break;
 
@@ -390,12 +390,6 @@ THREE.MTLLoader.MaterialCreator.prototype = {
 
 		}
 
-		if ( params[ 'diffuse' ] ) {
-
-			params[ 'color' ] = params[ 'diffuse' ];
-
-		}
-
 		this.materials[ materialName ] = new THREE.MeshPhongMaterial( params );
 		return this.materials[ materialName ];