[#59] morph: Adopt updated neo-go client API for subs

It does not use deprecated methods anymore but also adds more code that
removes. Future refactor that will affect more components will optimize
usage of the updated API.

Signed-off-by: Pavel Karpy <p.karpy@yadro.com>

pkg/morph/client/client.go

@@ -69,17 +69,12 @@ type Client struct {
 	// on every normal call.
 	switchLock *sync.RWMutex
 
-	// channel for ws notifications
 	notifications chan rpcclient.Notification
+	subsInfo      // protected with switchLock
 
 	// channel for internal stop
 	closeChan chan struct{}
 
-	// cached subscription information
-	subscribedEvents       map[util.Uint160]string
-	subscribedNotaryEvents map[util.Uint160]string
-	subscribedToNewBlocks  bool
-
 	// indicates that Client is not able to
 	// establish connection to any of the
 	// provided RPC endpoints