Mark SafeBrowsing.NotificationImageReporter.NetError as obsolete

Fixed: 1089423
Change-Id: Ib4e7f33dc6723aaecd28fe8b629991fb26ca07d8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2295403
Commit-Queue: Varun Khaneja <vakh@chromium.org>
Commit-Queue: Alexei Svitkine <asvitkine@chromium.org>
Auto-Submit: Varun Khaneja <vakh@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#787849}

tools/metrics/histograms/histograms.xml

@@ -146060,6 +146060,9 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 
 <histogram name="SafeBrowsing.NotificationImageReporter.NetError"
     enum="NetErrorCodes" expires_after="M85">
+  <obsolete>
+    Removed in M85+.
+  </obsolete>
   <owner>vakh@chromium.org</owner>
   <owner>chrome-safebrowsing-alerts@google.com</owner>
   <summary>