Remove eugenebut from UKM.IOSLog.OnSuccess histogram owners

Change-Id: I9d2be54c92815a0dffcf1c01c28c537a0ff6839d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2638784Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Commit-Queue: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845268}

tools/metrics/histograms/histograms_xml/ukm/histograms.xml

@@ -136,7 +136,6 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 
 <histogram name="UKM.IOSLog.OnSuccess" units="records"
     expires_after="2021-07-11">
-  <owner>eugenebut@chromium.org</owner>
   <owner>rkaplow@chromium.org</owner>
   <summary>
     Number of times when UKM.LogSize.OnSuccess was recorded on iOS. Recorded