Keep collecting Cr50 BoardIDFlags metrics

This information is of interest, especially in case of Board ID flags
misconfiguration incidents.

BUG=chromium:1089267
TEST=none

Change-Id: Ib93b0df5b58d08e72a1075a56c1bff24df53f6ef
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2446196Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Vadim Bendebury <vbendeb@chromium.org>
Auto-Submit: Vadim Bendebury <vbendeb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#818742}

tools/metrics/histograms/histograms_xml/platform/histograms.xml

@@ -166,7 +166,8 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Platform.Cr50.BoardIdFlags" enum="Cr50BoardIdFlags"
-    expires_after="M85">
+    expires_after="2021-10-18">
+  <owner>apronin@chromium.org</owner>
   <owner>vbendeb@chromium.org</owner>
   <summary>
     A sparse histogram of values of Board ID flags programmed in H1 devices in