Update OWNERS: remove inactive members, promote filzzp sbueringer

Signed-off-by: Vince Prignano <[email protected]>

Author: vincepri

OWNERS_ALIASES

@@ -4,9 +4,8 @@ aliases:
   # active folks who can be contacted to perform admin-related
   # tasks on the repo, or otherwise approve any PRS.
   controller-runtime-admins:
-  - droot
-  - mengqiy
-  - pwittrock
+  - vincepri
+  - joelanford
 
   # non-admin folks who have write-access and can approve any PRs in the repo
   controller-runtime-maintainers:
@@ -18,6 +17,8 @@ aliases:
   - gerred
   - shawn-hurley
   - alvaroaleman
+  - fillzpp
+  - sbueringer
 
   # folks who can review and LGTM any PRs in the repo (doesn't
   # include approvers & admins -- those count too via the OWNERS