Item: removed isTool()

this should be replaced with `instanceof Tool`.

src/pocketmine/item/Item.php

@@ -724,13 +724,6 @@ class Item implements ItemIds, \JsonSerializable{
 		return false;
 	}
 
-	/**
-	 * @return bool
-	 */
-	public function isTool(){
-		return false;
-	}
-
 	/**
 	 * Returns what type of block-breaking tool this is. Blocks requiring the same tool type as the item will break
 	 * faster (except for blocks requiring no tool, which break at the same speed regardless of the tool used)