remove 'history' batch type

This was from ircv3-specifications #362, which is now obsolete.

irc/responsebuffer.go

@@ -25,7 +25,7 @@ const (
 type ResponseBuffer struct {
 	Label     string // label if this is a labeled response batch
 	batchID   string // ID of the labeled response batch, if one has been initiated
-	batchType string // type of the labeled response batch (possibly `history` or `chathistory`)
+	batchType string // type of the labeled response batch (currently either `labeled-response` or `chathistory`)
 
 	// stack of batch IDs of nested batches, which are handled separately
 	// from the underlying labeled-response batch. starting a new nested batch
@@ -200,9 +200,7 @@ func (rb *ResponseBuffer) EndNestedBatch(batchID string) {
 // supported by the client (`history`, `chathistory`, or no batch, in descending order).
 func (rb *ResponseBuffer) StartNestedHistoryBatch(params ...string) (batchID string) {
 	var batchType string
-	if rb.session.capabilities.Has(caps.EventPlayback) {
-		batchType = "history"
-	} else if rb.session.capabilities.Has(caps.Batch) {
+	if rb.session.capabilities.Has(caps.Batch) {
 		batchType = "chathistory"
 	}
 	if batchType != "" {