Revert examples/jsm/exporters/GLTFExporter.js per review comments

examples/jsm/exporters/GLTFExporter.js

@@ -1188,16 +1188,6 @@ GLTFExporter.prototype = {
 				var attribute = geometry.attributes[ attributeName ];
 				attributeName = nameConversion[ attributeName ] || attributeName.toUpperCase();
 
-				// Prefix all geometry attributes except the ones specifically
-				// listed in the spec; non-spec attributes are considered custom.
-				var validVertexAttributes =
-						/^(POSITION|NORMAL|TANGENT|TEXCOORD_\d+|COLOR_\d+|JOINTS_\d+|WEIGHTS_\d+)$/;
-				if ( ! validVertexAttributes.test( attributeName ) ) {
-
-					attributeName = '_' + attributeName;
-
-				}
-
 				if ( cachedData.attributes.has( attribute ) ) {
 
 					attributes[ attributeName ] = cachedData.attributes.get( attribute );