Clean obsolete previews histograms.

Bug: 1089314, 1089312,1089310
Change-Id: I3cd2b0113e850e9b3795cea08a011c7060559f48
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2441377
Auto-Submit: Michael Crouse <mcrouse@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Commit-Queue: Michael Crouse <mcrouse@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812990}

tools/metrics/histograms/histograms_xml/histogram_suffixes_list.xml

@@ -4413,6 +4413,9 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram_suffixes>
 
 <histogram_suffixes name="DataSaverEnabled" separator=".">
+  <obsolete>
+    Obsolete as of 09/2020.
+  </obsolete>
   <suffix name="DataSaverDisabled" label="Data Saver is disabled"/>
   <suffix name="DataSaverEnabled" label="Data Saver is enabled"/>
   <affected-histogram name="Previews.ContentLength"/>

tools/metrics/histograms/histograms_xml/others/histograms.xml

@@ -10275,6 +10275,9 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Previews.ContentLength" units="KB" expires_after="M85">
+  <obsolete>
+    Not even logged by code. Obsolete in 09/2020.
+  </obsolete>
   <owner>ryansturm@chromium.org</owner>
   <summary>
     The actual data used for a page load using a preview optimization.
@@ -10306,6 +10309,9 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Previews.DataSavings" units="KB" expires_after="M85">
+  <obsolete>
+    Obsolete as of 09/2020.
+  </obsolete>
   <owner>ryansturm@chromium.org</owner>
   <summary>
     The estimated data savings for a page load using a previews optimization.
@@ -10315,6 +10321,9 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Previews.DataSavingsPercent" units="%" expires_after="M85">
+  <obsolete>
+    Obsolete as of 09/2020.
+  </obsolete>
   <owner>ryansturm@chromium.org</owner>
   <summary>
     The estimated percent of data savings for a page load using a previews
@@ -10382,6 +10391,9 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Previews.OriginalContentLength" units="KB" expires_after="M85">
+  <obsolete>
+    Not even logged by code. Obsolete in 09/2020.
+  </obsolete>
   <owner>ryansturm@chromium.org</owner>
   <summary>
     The estimated content length of a page load using a preview optimization.