Subscription remove unused instance class member

src/modules/uORB/Subscription.cpp

@@ -43,8 +43,7 @@ namespace uORB
 {
 
 SubscriptionBase::SubscriptionBase(const struct orb_metadata *meta, unsigned interval, unsigned instance) :
-	_meta(meta),
-	_instance(instance)
+	_meta(meta)
 {
 	if (instance > 0) {
 		_handle = orb_subscribe_multi(_meta, instance);

src/modules/uORB/Subscription.hpp

@@ -85,7 +85,6 @@ public:
 
 protected:
 	const struct orb_metadata *_meta;
-	unsigned _instance;
 	int _handle;
 };