* Update whats-new-in-v7-2.md

Grafana 7.2.0 was released 2020-09-23 and isn't in beta anymore, see https://github.com/grafana/grafana/blob/master/CHANGELOG.md

* Update docs/sources/guides/whats-new-in-v7-2.md

Remove warning about article being incomplete

Co-authored-by: Emil Tullstedt <emil.tullstedt@grafana.com>

Co-authored-by: Emil Tullstedt <emil.tullstedt@grafana.com>