remove redundant code

examples/async.js

@@ -1,12 +1,12 @@
 let cls = require('../index');
-
-let context = cls.create('myContext');
+let key = Symbol();
+let context = cls.create(key);
 context.run(() => {
 	context.name = 'George';
 	setTimeout(onTimeout, 300);
 });
 
 function onTimeout() {
-	let context = cls.get('myContext');
+	let context = cls.get(key);
 	console.log(context.name); //George
 }

index-core.js

@@ -134,8 +134,7 @@ function init(asyncId, _type, triggerId) {
 }
 
 function log(str) {
-	if (cls.debug)
-		fs.writeSync(1, `${str}\n`);
+	fs.writeSync(1, `${str}\n`);
 }
 
 function destroy(asyncId) {
@@ -145,8 +144,6 @@ function destroy(asyncId) {
 		log(`destroy ${  asyncId} : ${  Object.keys(stack).length}`);
 		log(`keys ${  Object.keys(stack)}`);
 	}
-
-	delete stack[asyncId];
 }
 
 module.exports = cls;