VOL-2920 - Remove NBI passthrough functions.

Modified the NBIHandler to reference device, logical device, and adapter managers as embedded types, allowing the managers to directly implement API functions, without the need for individual passthrough functions.
Also created a new event.Manager type, which is embedded in device.LogicalManager.
Also renamed device.NewDeviceManagers() to device.NewManagers().

Change-Id: I8455da79b991ee67cc16cf898b00b0c98ea97bcd
diff --git a/rw_core/core/core.go b/rw_core/core/core.go
index de126a2..7cf9f98 100644
--- a/rw_core/core/core.go
+++ b/rw_core/core/core.go
@@ -122,7 +122,7 @@
 
 	logger.Debugw("values", log.Fields{"kmp": core.kmp})
 	core.adapterMgr = adapter.NewAdapterManager(core.clusterDataProxy, core.instanceID, core.kafkaClient)
-	core.deviceMgr, core.logicalDeviceMgr = device.NewDeviceManagers(core.clusterDataProxy, core.adapterMgr, core.kmp, endpointMgr, core.config.CorePairTopic, core.instanceID, core.config.DefaultCoreTimeout)
+	core.deviceMgr, core.logicalDeviceMgr = device.NewManagers(core.clusterDataProxy, core.adapterMgr, core.kmp, endpointMgr, core.config.CorePairTopic, core.instanceID, core.config.DefaultCoreTimeout)
 
 	// Start the KafkaManager. This must be done after the deviceMgr, adapterMgr, and
 	// logicalDeviceMgr have been created, as once the kmp is started, it will register
@@ -172,9 +172,8 @@
 	core.grpcServer = grpcserver.NewGrpcServer(core.config.GrpcHost, core.config.GrpcPort, nil, false, probe.GetProbeFromContext(ctx))
 	logger.Info("grpc-server-created")
 
-	core.grpcNBIAPIHandler = api.NewAPIHandler(core.deviceMgr, core.logicalDeviceMgr, core.adapterMgr)
+	core.grpcNBIAPIHandler = api.NewNBIHandler(core.deviceMgr, core.logicalDeviceMgr, core.adapterMgr)
 	logger.Infow("grpc-handler", log.Fields{"core_binding_key": core.config.CoreBindingKey})
-	core.logicalDeviceMgr.SetEventCallbacks(core.grpcNBIAPIHandler)
 	//	Create a function to register the core GRPC service with the GRPC server
 	f := func(gs *grpc.Server) {
 		voltha.RegisterVolthaServiceServer(