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/NetherBrick.php

@@ -32,15 +32,11 @@ class NetherBrick extends Solid{
 		return BlockToolType::TYPE_PICKAXE;
 	}
 
+	public function getToolHarvestLevel() : int{
+		return TieredTool::TIER_WOODEN;
+	}
+
 	public function getHardness() : float{
 		return 2;
 	}
-
-	public function getDrops(Item $item) : array{
-		if($item->isPickaxe() >= TieredTool::TIER_WOODEN){
-			return parent::getDrops($item);
-		}
-
-		return [];
-	}
 }