Remove Grafana reset logic during upgrade in GitLab 13.0
For upgrading to 13.0, users will have to be on last version of 12.x, by which they would've already done a Grafana reset (as part of https://gitlab.com/gitlab-org/omnibus-gitlab/-/issues/4596). So we can safely remove the logic from the codebase.
Edited by Balasankar 'Balu' C