OWNERS: Remove obsolete entries

Remove colleagues who don't work on these projects anymore.

Change-Id: I37f9d55d6af78102ce6b6efc4159d543f01af603
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2235076Reviewed-by: Alexander Hendrich <hendrich@chromium.org>
Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Commit-Queue: Maksim Ivanov <emaxx@chromium.org>
Cr-Commit-Position: refs/heads/master@{#775993}

chrome/browser/chromeos/extensions/login_screen/OWNERS

 hendrich@chromium.org
 jityao@google.com
-voit@google.com

chrome/browser/chromeos/login/saml/OWNERS

@@ -2,5 +2,4 @@
 xiyuan@chromium.org
 
 # (in CET)
-olsen@chromium.org
 rsorokin@chromium.org

chrome/browser/resources/chromeos/password_change/OWNERS

-olsen@chromium.org
 rsorokin@chromium.org

chrome/browser/ui/webui/chromeos/in_session_password_change/OWNERS

-olsen@chromium.org
 rsorokin@chromium.org