Mark MCSP responses as NOT_IMPLEMENTED (#14853)

* Validate session type before trying  to cast and return the secure session counter

* Completely remove the counter response: MCSP not yet implemented for groups it seems

* Fix typo

src/protocols/secure_channel/MessageCounterManager.cpp

@@ -222,26 +222,20 @@ CHIP_ERROR MessageCounterManager::SendMsgCounterSyncResp(Messaging::ExchangeCont
                                                          FixedByteSpan<kChallengeSize> challenge)
 {
     System::PacketBufferHandle msgBuf;
-
     VerifyOrDie(exchangeContext->HasSessionHandle());
 
-    // Allocate new buffer.
-    msgBuf = MessagePacketBuffer::New(kSyncRespMsgSize);
-    VerifyOrReturnError(!msgBuf.IsNull(), CHIP_ERROR_NO_MEMORY);
-
-    {
-        uint8_t * msg = msgBuf->Start();
-        Encoding::LittleEndian::BufferWriter bbuf(msg, kSyncRespMsgSize);
-        bbuf.Put32(
-            exchangeContext->GetSessionHandle()->AsSecureSession()->GetSessionMessageCounter().GetLocalMessageCounter().Value());
-        bbuf.Put(challenge.data(), kChallengeSize);
-        VerifyOrReturnError(bbuf.Fit(), CHIP_ERROR_NO_MEMORY);
-    }
+    VerifyOrReturnError(exchangeContext->GetSessionHandle()->GetSessionType() == Transport::Session::SessionType::kGroup,
+                        CHIP_ERROR_INVALID_ARGUMENT);
 
-    msgBuf->SetDataLength(kSyncRespMsgSize);
+    // NOTE: not currently implemented. When implementing, the following should be done:
+    //    - allocate a new buffer: MessagePacketBuffer::New
+    //    - setup payload and place the local message counter + challange in it
+    //    - exchangeContext->SendMessage(Protocols::SecureChannel::MsgType::MsgCounterSyncRsp, ...)
+    //
+    // You can view the history of this file for a partial implementation that got
+    // removed due to it using non-group sessions.
 
-    return exchangeContext->SendMessage(Protocols::SecureChannel::MsgType::MsgCounterSyncRsp, std::move(msgBuf),
-                                        Messaging::SendFlags(Messaging::SendMessageFlags::kNoAutoRequestAck));
+    return CHIP_ERROR_NOT_IMPLEMENTED;
 }
 
 CHIP_ERROR MessageCounterManager::HandleMsgCounterSyncReq(Messaging::ExchangeContext * exchangeContext,