[Paint Preview] Obsolete CaptureExperiment histograms

The capture experiment was removed in:
https://chromium-review.googlesource.com/c/chromium/src/+/2299184

However, some histogram deletions were missed. This CL makes those
histograms obsolete.

Bug: 1147100
Change-Id: Ie6d5f5d917ac1d7f14302648bbbc279ac745f263
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2544046Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Calder Kitagawa <ckitagawa@chromium.org>
Cr-Commit-Position: refs/heads/master@{#829270}

tools/metrics/histograms/histograms_xml/browser/histograms.xml

@@ -117,6 +117,10 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 
 <histogram name="Browser.PaintPreview.CaptureExperiment.CompressedOnDiskSize"
     units="KB" expires_after="2020-12-20">
+  <obsolete>
+    Obsoleted on 2020-11-17 as corresponding experiment code was removed and the
+    experiment wrapped up.
+  </obsolete>
   <owner>ckitagawa@chromium.org</owner>
   <owner>mahmoudi@chromium.org</owner>
   <owner>fredmello@chromium.org</owner>
@@ -128,6 +132,10 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 
 <histogram name="Browser.PaintPreview.CaptureExperiment.Success"
     enum="BooleanSuccess" expires_after="2020-12-20">
+  <obsolete>
+    Obsoleted on 2020-11-17 as corresponding experiment code was removed and the
+    experiment wrapped up.
+  </obsolete>
   <owner>ckitagawa@chromium.org</owner>
   <owner>mahmoudi@chromium.org</owner>
   <owner>fredmello@chromium.org</owner>