Do not import an unused proto file

onos-buck test --only-failing gives me the following warning:

net/packet/PacketServiceNb.proto: warning: Import
net/flow/TrafficTreatmentProto.proto but not used.

Change-Id: If847fe8d0110550999a1aef9646ae59d86524765
diff --git a/incubator/protobuf/services/nb/src/main/proto/net/packet/PacketServiceNb.proto b/incubator/protobuf/services/nb/src/main/proto/net/packet/PacketServiceNb.proto
index 26d6c90..d048d0a 100644
--- a/incubator/protobuf/services/nb/src/main/proto/net/packet/PacketServiceNb.proto
+++ b/incubator/protobuf/services/nb/src/main/proto/net/packet/PacketServiceNb.proto
@@ -9,7 +9,6 @@
 import "net/packet/OutboundPacketProto.proto";
 import "core/ApplicationIdProto.proto";
 import "net/flow/TrafficSelectorProto.proto";
-import "net/flow/TrafficTreatmentProto.proto";
 
 message addProcessorRequest {
     .net.packet.PacketProcessorProto packet_processor = 1;