Extend UMA histogram expiration for re-registration results

Actively purging non-ephemeral user sessions will only start in
2020/2021 (still in discussion), since we only started recording last
activities since 2019-01-29.

Bug: 870616
Change-Id: I8ec9cd05a77ec7e4068fa380afeb64931535c31f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1985010
Auto-Submit: Alexander Hendrich <hendrich@chromium.org>
Reviewed-by: Sergey Poromov <poromov@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Steven Holte <holte@chromium.org>
Cr-Commit-Position: refs/heads/master@{#731814}

tools/metrics/histograms/histograms.xml

@@ -42090,8 +42090,10 @@ uploading your change for review.
 </histogram>
 
 <histogram name="Enterprise.UserPolicyChromeOS.ReregistrationResult"
-    enum="EnterpriseUserPolicyChromeOSReregistrationResult" expires_after="M81">
+    enum="EnterpriseUserPolicyChromeOSReregistrationResult"
+    expires_after="2022-01-31">
   <owner>hendrich@chromium.org</owner>
+  <owner>managed-devices@google.com</owner>
   <summary>Re-registration results after failed policy fetch.</summary>
 </histogram>