[VOL-3107] Add DeleteGroup API to OpenOLT Agent

- DeleteGroup proto API method implemented.
- Unit tests added.

Change-Id: If196a92f7a717fc4cc6c2f0e0bb6ca74fc3683d2
diff --git a/agent/common/server.cc b/agent/common/server.cc
index 17b804e..baeb590 100644
--- a/agent/common/server.cc
+++ b/agent/common/server.cc
@@ -309,6 +309,13 @@
         return PerformGroupOperation_(request);
     };
 
+    Status DeleteGroup(
+            ServerContext* context,
+            const openolt::Group* request,
+            openolt::Empty* response) override {
+        return DeleteGroup_(request->group_id());
+    };
+
     Status OnuItuPonAlarmSet(
             ServerContext* context,
             const openolt::OnuItuPonAlarm* request,