fix: remove duplicate sync func

[ronething]

Type of change:

• Bugfix
• New feature provided
• Improve performance
• Backport patches
• Documentation
• Refactor
• Chore
• CI/CD or Tests

What this PR does / why we need it:

In the Start function of adc client, we have already implemented the matter of timed synchronization, and there is no need to open a new go func for the same processing.

ref:

apisix-ingress-controller/internal/provider/adc/adc.go

Lines 297 to 321 in a3bb208

	func (d *adcClient) Start(ctx context.Context) error {
	initalSyncDelay := d.InitSyncDelay
	time.AfterFunc(initalSyncDelay, func() {
	if err := d.Sync(ctx); err != nil {
	log.Error(err)
	return
	}
	})
	if d.SyncPeriod < 1 {
	return nil
	}
	ticker := time.NewTicker(d.SyncPeriod)
	defer ticker.Stop()
	for {
	select {
	case <-ticker.C:
	if err := d.Sync(ctx); err != nil {
	log.Error(err)
	}
	case <-ctx.Done():
	return nil
	}
	}
	}

Pre-submission checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?
• Is this PR backward compatible? If it is not backward compatible, please discuss on the mailing list first