l2geth: cleanup `time.Ticker`s in `SyncService`

Simply clean up the `time.Ticker`s using `defer t.Close()`.
Not having this code should not cause any problems, but
it is best practice to close the tickers as not doing so
can result in memory leaks in certain cases.

.changeset/big-files-smoke.md

+---
+'@eth-optimism/l2geth': patch
+---
+
+Cleanup `time.Ticker`s

l2geth/rollup/sync_service.go

@@ -359,6 +359,7 @@ func (s *SyncService) Stop() error {
 func (s *SyncService) VerifierLoop() {
 	log.Info("Starting Verifier Loop", "poll-interval", s.pollInterval, "timestamp-refresh-threshold", s.timestampRefreshThreshold)
 	t := time.NewTicker(s.pollInterval)
+	defer t.Stop()
 	for ; true; <-t.C {
 		if err := s.verify(); err != nil {
 			log.Error("Could not verify", "error", err)
@@ -387,6 +388,7 @@ func (s *SyncService) verify() error {
 func (s *SyncService) SequencerLoop() {
 	log.Info("Starting Sequencer Loop", "poll-interval", s.pollInterval, "timestamp-refresh-threshold", s.timestampRefreshThreshold)
 	t := time.NewTicker(s.pollInterval)
+	defer t.Stop()
 	for ; true; <-t.C {
 		s.txLock.Lock()
 		if err := s.sequence(); err != nil {