Merge pull request #56199 from langyenan/gce

Automatic merge from submit-queue (batch tested with PRs 54410, 56184, 56199, 56191, 56231). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Delete unused code in gce/ensureInternalBackendService

existingIGLinks is not used after initialization,  because instance groups are compared in backendSvcEqual()

**Release note**:
```release-note
NONE
```

/area cloudprovider
/area platform/gce
/sig gcp

pkg/cloudprovider/providers/gce/gce_loadbalancer_internal.go

@@ -525,11 +525,6 @@ func (gce *GCECloud) ensureInternalBackendService(name, description string, affi
 		glog.V(2).Infof("ensureInternalBackendService: created backend service %v successfully", name)
 		return nil
 	}
-	// Check existing backend service
-	existingIGLinks := sets.NewString()
-	for _, be := range bs.Backends {
-		existingIGLinks.Insert(be.Group)
-	}
 
 	if backendSvcEqual(expectedBS, bs) {
 		return nil