Added harvest level properties to applicable blocks

this fixes block-breaking animations with wrong tools, and also finally resolves the long-standing hierarchy problem in Stair.

src/pocketmine/block/WoodenStairs.php

@@ -39,11 +39,4 @@ class WoodenStairs extends Stair{
 	public function getToolType() : int{
 		return BlockToolType::TYPE_AXE;
 	}
-
-	public function getDrops(Item $item) : array{
-		//TODO: Hierarchy problem (base class is for stone stairs)
-		return [
-			ItemFactory::get($this->getItemId(), $this->getVariant(), 1)
-		];
-	}
 }