perf(DefaultScheduler): remove setting of timer property

setTimeout() reference was being saved for no reason

src/lib/DefaultScheduler.ts

@@ -35,10 +35,9 @@ class Periodic implements Subscription {
 }
 class Delay implements Subscription {
   closed = false
-  private timer: number
 
   constructor (private task: ITask, private timeout: number) {
-    this.timer = setTimeout(this.onEvent.bind(this), this.timeout) as any as number
+    setTimeout(this.onEvent.bind(this), this.timeout)
   }
 
   private onEvent () {