Fix nits leftover from WMPA MSE deletion.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index e4e29aeeb7dda960671391a639ab42e29e5de9e1..44262bd6941005060724f7e893ff76d98a9335b8 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -23721,6 +23721,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 
 <histogram name="Media.MSE.LateAudioFrames"
     units="late frames per million frames">
+  <obsolete>
+    Deleted along with browser side MSE implementation.
+  </obsolete>
   <owner>qinmin@chromium.org</owner>
   <owner>timav@chromium.org</owner>
   <summary>
@@ -23733,6 +23736,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 
 <histogram name="Media.MSE.LateVideoFrames"
     units="late frames per million frames">
+  <obsolete>
+    Deleted along with browser side MSE implementation.
+  </obsolete>
   <owner>qinmin@chromium.org</owner>
   <owner>timav@chromium.org</owner>
   <summary>
@@ -23763,6 +23769,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="Media.MSE.PlaybackDuration" units="ms">
+  <obsolete>
+    Deleted along with browser side MSE implementation.
+  </obsolete>
   <owner>qinmin@chromium.org</owner>
   <owner>timav@chromium.org</owner>
   <summary>
@@ -23774,6 +23783,9 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="Media.MSE.Starvations" units="starvations per million frames">
+  <obsolete>
+    Deleted along with browser side MSE implementation.
+  </obsolete>
   <owner>qinmin@chromium.org</owner>
   <owner>timav@chromium.org</owner>
   <summary>