Remove old contributors from OWNERS file, add new ones (#1128)

We are refreshing the list of maintainers to keep it aligned with
the current state of contributions, removing accounts who haven't contributed in
the past year.

Thanks @mariomac @eranra @KalmanMeth and @ronensc for your contributions!
You are of course welcome to come back if you wish :-)

Author: jotak

OWNERS

@@ -1,19 +1,13 @@
 approvers:
-- mariomac
 - jotak
 - jpinsonneau
 - OlivierCazade
-- eranra
-- KalmanMeth
-- ronensc
 - stleerh
+- luisjira
+- leandroberetta
 options: {}
 reviewers:
-- mariomac
 - jotak
 - jpinsonneau
 - OlivierCazade
 - stleerh
-- eranra
-- KalmanMeth
-- ronensc