channeldb+rpcserver: return number of deleted payments

rpcserver.go

@@ -7319,7 +7319,7 @@ func (r *rpcServer) DeleteAllPayments(ctx context.Context,
 		"failed_htlcs_only=%v", req.FailedPaymentsOnly,
 		req.FailedHtlcsOnly)
 
-	err := r.server.miscDB.DeletePayments(
+	_, err := r.server.miscDB.DeletePayments(
 		req.FailedPaymentsOnly, req.FailedHtlcsOnly,
 	)
 	if err != nil {