Obsolete long-dead Stability.ExitFunnel histogram.

Bug: 1089528
Change-Id: I525693ed054e3c8d33bba6d6ee68ae3c8b82833d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2485514
Commit-Queue: Sigurður Ásgeirsson <siggi@chromium.org>
Auto-Submit: Sigurður Ásgeirsson <siggi@chromium.org>
Reviewed-by: Weilun Shi <sweilun@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819358}

tools/metrics/histograms/histograms_xml/stability/histograms.xml

@@ -240,6 +240,9 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Stability.ExitFunnel" units="ms" expires_after="M85">
+  <obsolete>
+    Removed 10/2020 although this has been dead for many years.
+  </obsolete>
   <owner>siggi@chromium.org</owner>
   <summary>
     Temporary instrumentation to record the Windows browser's exit path. See