Remove Julius (myself) from maintainers (#1831)

My last commit was 1.5 years ago, and I haven't been active on Cortex
since then.

Signed-off-by: Julius Volz <julius.volz@gmail.com>

Author: juliusv

MAINTAINERS

@@ -2,7 +2,6 @@ Bryan Boreham, Weaveworks <bryan@weave.works> (@bboreham)
 Chris Marchbanks, independent <csmarchbanks@gmail.com> (@csmarchbanks)
 Cody Boggs, independent <strofcon@gmail.com> (@cboggs)
 Jacob Lisi, Grafana Labs <jacob.t.lisi@gmail.com> (@jtlisi)
-Julius Volz, independent <julius.volz@gmail.com> (@juliusv)
 Ken Haines, Microsoft <khaines@microsoft.com> (@khaines)
 Tom Wilkie, Grafana Labs <tom.wilkie@gmail.com> (@tomwilkie)
 Goutham Veeramachaneni, Grafana Labs <gouthamve@gmail.com> (@gouthamve)