DistributedFlowRuleStore: support remote removeFlowRule needed for cancelling Batch

Change-Id: I40f8dd8c2008e93c5ac7393295374726f83353c7
diff --git a/core/store/dist/src/main/java/org/onlab/onos/store/flow/impl/FlowStoreMessageSubjects.java b/core/store/dist/src/main/java/org/onlab/onos/store/flow/impl/FlowStoreMessageSubjects.java
index a1cee06..bc60673 100644
--- a/core/store/dist/src/main/java/org/onlab/onos/store/flow/impl/FlowStoreMessageSubjects.java
+++ b/core/store/dist/src/main/java/org/onlab/onos/store/flow/impl/FlowStoreMessageSubjects.java
@@ -31,4 +31,7 @@
 
     public static final MessageSubject GET_DEVICE_FLOW_ENTRIES
         = new MessageSubject("peer-forward-get-device-flow-entries");
+
+    public static final MessageSubject REMOVE_FLOW_ENTRY
+        = new MessageSubject("peer-forward-remove-flow-entry");
 }