rpcclient: fix comment nits

- delete TODO related to clearing batch list;
- refine comment for code when batchList len is 0

rpcclient/infrastructure.go

@@ -1669,7 +1669,7 @@ func (c *Client) sendAsync() (FutureGetBulkResult, error) {
 	c.batchLock.Lock()
 	defer c.batchLock.Unlock()
 
-	// if batchlist is empty, there's nothing to send
+	// If batchList is empty, there's nothing to send.
 	if c.batchList.Len() == 0 {
 		return nil, ErrEmptyBatch
 	}
@@ -1709,10 +1709,6 @@ func (c *Client) Send() error {
 	batchResp, err := future.Receive()
 	if err != nil {
 		// Clear batchlist in case of an error.
-		//
-		// TODO(yy): need to double check to make sure there's no
-		// concurrent access to this batch list, otherwise we may miss
-		// some batched requests.
 
 		c.batchLock.Lock()
 		c.batchList = list.New()