Removed @deprecated classes, methods and properties, added some type hints

src/pocketmine/scheduler/AsyncTask.php

@@ -49,15 +49,6 @@ abstract class AsyncTask extends \Collectable{
 		$this->setGarbage();
 	}
 
-	/**
-	 * @deprecated
-	 *
-	 * @return bool
-	 */
-	public function isFinished(){
-		return $this->isGarbage();
-	}
-
 	/**
 	 * @return mixed
 	 */