In current ThreadSafeUnaligner, the variable `storeNewBuffers` has actually two usages. One is for avoiding duplicated counter for processing barrier or notifying received barrier for a respective channel. Another usage is for judging whether the notified buffer should be spilled by writer or not.
In RemoteInputChannel, we already have the states of `lastRequestedCheckpointId` and `receivedCheckpointId` to control whether the received buffer should be notified to unaligner component. In other words, as long as the `RemoteInputChannel` decides to notify this received buffer, it should be always needed to spill in ThreadSafeUnaligner. So we can remove the related condition inside ThreadSafeUnaligner#notifyBufferReceived and make the semantic of `storeNewBuffers` more clearly.