ClientDataToSkinDataHelper: Remove SingletonTrait

SingletonTrait is pointless here for multiple reasons:
1) the class is final
2) this is protocol-specific translation of types, no loss of data or alternative mutation of it needs to occur

Using SingletonTrait is an obstacle to separating the protocol library from the core code, so it has to go.

src/types/login/ClientDataToSkinDataHelper.php

@@ -28,12 +28,10 @@
 use pocketmine\network\mcpe\protocol\types\skin\SkinAnimation;
 use pocketmine\network\mcpe\protocol\types\skin\SkinData;
 use pocketmine\network\mcpe\protocol\types\skin\SkinImage;
-use pocketmine\utils\SingletonTrait;
 use function array_map;
 use function base64_decode;
 
 final class ClientDataToSkinDataHelper{
-	use SingletonTrait;
 
 	/**
 	 * @throws \InvalidArgumentException
@@ -49,7 +47,7 @@ private static function safeB64Decode(string $base64, string $context) : string{
 	/**
 	 * @throws \InvalidArgumentException
 	 */
-	public function fromClientData(ClientData $clientData) : SkinData{
+	public static function fromClientData(ClientData $clientData) : SkinData{
 		/** @var SkinAnimation[] $animations */
 		$animations = [];
 		foreach($clientData->AnimatedImageData as $k => $animation){