Removed bad assumption that every Flowable descendent is an instant-breaking block

I'm wondering if there is even a point to Flowable at this point. Half of the blocks inheriting from it do not break instantly, or have some other modification to tool requirements.

src/pocketmine/block/Crops.php

@@ -36,6 +36,10 @@ abstract class Crops extends Flowable{
 	/** @var int */
 	protected $age = 0;
 
+	public function __construct(BlockIdentifier $idInfo, string $name, ?BlockBreakInfo $breakInfo = null){
+		parent::__construct($idInfo, $name, $breakInfo ?? BlockBreakInfo::instant());
+	}
+
 	protected function writeStateToMeta() : int{
 		return $this->age;
 	}