avoid direct mutation of Item->count field, use Item->pop() instead

I think this change was already applied on the master branch, but I don't remember for sure.

src/pocketmine/block/Crops.php

@@ -55,7 +55,7 @@ abstract class Crops extends Flowable{
 				$this->getLevel()->setBlock($this, $ev->getNewState(), true, true);
 			}
 
-			$item->count--;
+			$item->pop();
 
 			return true;
 		}

src/pocketmine/block/Grass.php

@@ -99,7 +99,7 @@ class Grass extends Solid{
 
 	public function onActivate(Item $item, Player $player = null) : bool{
 		if($item->getId() === Item::DYE and $item->getDamage() === 0x0F){
-			$item->count--;
+			$item->pop();
 			TallGrassObject::growGrass($this->getLevel(), $this, new Random(mt_rand()), 8, 2);
 
 			return true;

src/pocketmine/block/Sapling.php

@@ -72,7 +72,7 @@ class Sapling extends Flowable{
 			//TODO: change log type
 			Tree::growTree($this->getLevel(), $this->x, $this->y, $this->z, new Random(mt_rand()), $this->getVariant());
 
-			$item->count--;
+			$item->pop();
 
 			return true;
 		}

src/pocketmine/block/Sugarcane.php

@@ -62,7 +62,7 @@ class Sugarcane extends Flowable{
 				$this->getLevel()->setBlock($this, $this, true);
 			}
 
-			$item->count--;
+			$item->pop();
 
 			return true;
 		}

src/pocketmine/item/PaintingItem.php

@@ -96,7 +96,7 @@ class PaintingItem extends Item{
 		$entity = Entity::createEntity("Painting", $blockReplace->getLevel(), $nbt);
 
 		if($entity instanceof Entity){
-			--$this->count;
+			$this->pop();
 			$entity->spawnToAll();
 
 			$player->getLevel()->broadcastLevelEvent($blockReplace->add(0.5, 0.5, 0.5), LevelEventPacket::EVENT_SOUND_ITEMFRAME_PLACE); //item frame and painting have the same sound

src/pocketmine/item/ProjectileItem.php

@@ -54,7 +54,7 @@ abstract class ProjectileItem extends Item{
 			$projectile->setMotion($projectile->getMotion()->multiply($this->getThrowForce()));
 		}
 
-		$this->count--;
+		$this->pop();
 
 		if($projectile instanceof Projectile){
 			$projectileEv = new ProjectileLaunchEvent($projectile);

src/pocketmine/item/SpawnEgg.php

@@ -44,7 +44,7 @@ class SpawnEgg extends Item{
 		$entity = Entity::createEntity($this->meta, $player->getLevel(), $nbt);
 
 		if($entity instanceof Entity){
-			--$this->count;
+			$this->pop();
 			$entity->spawnToAll();
 			return true;
 		}