Delete old metadafa field when converting to new JSON schema

Revision for v0.8.10

src/Engine.js

@@ -584,16 +584,17 @@ Blackprint.Engine = class Engine extends CustomEvent {
 		console.error("The exported instance (JSON) format was deprecated, please re-export the JSON by importing your JSON to the editor and export it. Your current JSON format may not work after version v1.0. Other engine than JavaScript may also not support the old format.");
 
 		let newData = { instance: obj };
-
 		let metadata = obj._;
+		delete obj._;
+
 		if(metadata){
 			newData.moduleJS = metadata.moduleJS;
 			newData.functions = metadata.functions;
 			newData.variables = metadata.variables;
 			newData.events = metadata.events;
 			newData.environments = metadata.env;
 		}
-	
+
 		return newData;
 	}