Stepping down as maintainer (#4090)

Signed-off-by: Ken Haines <khaines@microsoft.com>

Author: khaines

MAINTAINERS

@@ -1,7 +1,6 @@
 Bryan Boreham, Weaveworks <bryan@weave.works> (@bboreham)
 Goutham Veeramachaneni, Grafana Labs <gouthamve@gmail.com> (@gouthamve)
 Jacob Lisi, Grafana Labs <jacob.t.lisi@gmail.com> (@jtlisi)
-Ken Haines, Microsoft <khaines@microsoft.com> (@khaines)
 Marco Pracucci, Grafana Labs <marco@pracucci.com> (@pracucci)
 Peter Štibraný, Grafana Labs <pstibrany@gmail.com> (@pstibrany)
 Tom Wilkie, Grafana Labs <tom.wilkie@gmail.com> (@tomwilkie)