Mark as obsolete some unused Cookie.* histograms

The code that logged to these histograms was deleted in 2017, but I forgot
to mark them as obsolete in histograms.xml.

Change-Id: Idbca14571c01f0c81a76478d8967dd7f18bb61c4
Bug: 736978
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1802709
Auto-Submit: Nick Harper <nharper@chromium.org>
Commit-Queue: Jesse Doherty <jwd@chromium.org>
Reviewed-by: Jesse Doherty <jwd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#696971}

tools/metrics/histograms/histograms.xml

@@ -24417,6 +24417,9 @@ uploading your change for review.
 </histogram>
 
 <histogram name="Cookie.DeletionCause" enum="CookieDeletionCause">
+  <obsolete>
+    Removed Jul 2017 for lack of use.
+  </obsolete>
   <owner>nharper@chromium.org</owner>
   <summary>
     For each cookie removed from the store, the reason it was removed.
@@ -24461,6 +24464,9 @@ uploading your change for review.
 </histogram>
 
 <histogram name="Cookie.EvictedLastAccessMinutes" units="minutes">
+  <obsolete>
+    Removed Jul 2017 for lack of use.
+  </obsolete>
   <owner>nharper@chromium.org</owner>
   <summary>
     For each evicted (not expired) cookie, the amount of time since it was last