vitessio#13175 is fixed, therefore re-instating on-deman heartbeats

Signed-off-by: Shlomi Noach <2607934+shlomi-noach@users.noreply.github.com>

go/test/endtoend/vreplication/cluster_test.go

@@ -412,13 +412,7 @@ func (vc *VitessCluster) AddTablet(t testing.TB, cell *Cell, keyspace *Keyspace,
 
 	options := []string{
 		"--queryserver-config-schema-reload-time", "5",
-		// Replace constant heartbeats (--heartbeat_enable) with the
-		// on-demand ones (--heartbeat_on_demand_duration=5s) once
-		// https://github.com/vitessio/vitess/issues/13175 is fixed.
-		// This is because rdonly or replica tablets will almost always
-		// be chosen as the vstreamers.
-		// "--heartbeat_on_demand_duration", "5s",
-		"--heartbeat_enable",
+		"--heartbeat_on_demand_duration", "5s",
 		"--heartbeat_interval", "250ms",
 	} // FIXME: for multi-cell initial schema doesn't seem to load without "--queryserver-config-schema-reload-time"
 	options = append(options, extraVTTabletArgs...)