Remove UMA collection no longer needed.

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 48d30ea85c42f0396ed2d4379aa81eb616561a78..2e355a6e3976a7bd1f009530c10411977d3609d8 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -21775,6 +21775,10 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 </histogram>
 
 <histogram name="JSDialogs.SiteEngagementOfDialogs" units="%">
+  <obsolete>
+    Deprecated 2016-10. Site engagement needed to be measured in small buckets
+    anyway so it was never high-resolution enough for use.
+  </obsolete>
   <owner>avi@chromium.org</owner>
   <summary>
     The site engagement values of sites showing dialogs. Logged once per dialog,
@@ -106150,6 +106154,9 @@ value.
 </histogram_suffixes>
 
 <histogram_suffixes name="JSDialogs.DialogType" separator=".">
+  <obsolete>
+    Deprecated 2016-10.
+  </obsolete>
   <suffix name="Alert"/>
   <suffix name="Confirm"/>
   <suffix name="Prompt"/>