Remove `gitops_sync` usage metric counter
What does this MR do and why?
Remove gitops_sync
usage metric counter
This change set removes the gitops_sync
usage metric counter that was
used by the deprecated GitOps module in the GitLab Agent for Kubernetes.
In GitLab 17.0 the GitOps module in the agent will be removed and so can this counter.
Depends on: #406545 (closed)
All associated merge requests of #406545 (closed) need to be merged, released and running in production before this change set can be merged.