Use registered users in system/update_engine OWNERS files.

AOSP project owners should be registered in Gerrit Code Review.

Bug: 33166666
Test: default build targets
Change-Id: I31df544212f565c60c848d92cd6ef984d5d0b475
diff --git a/OWNERS b/OWNERS
index fafbecc..f64bd32 100644
--- a/OWNERS
+++ b/OWNERS
@@ -1,4 +1,8 @@
 set noparent
-deymo@chromium.org
-garnold@chromium.org
-zeuthen@chromium.org
+
+# Current general maintainers:
+deymo@google.com
+senj@google.com
+
+# Chromium OS maintainers:
+benchan@google.com