Keep the Ash.NightLight.DisplayCrtcCtmSupport histograms until after M79

This is a useful histogram, so postpone its expiry until after M79.

BUG=975200

Change-Id: Id6b8c2b5d76d1c65cc8dac1291ab0eaaa74e1494
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1691867Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#675793}

tools/metrics/histograms/histograms.xml

@@ -6262,7 +6262,7 @@ uploading your change for review.
 </histogram>
 
 <histogram name="Ash.NightLight.DisplayCrtcCtmSupport"
-    enum="AshNightLightDisplayCrtcCtmSupportType" expires_after="M77">
+    enum="AshNightLightDisplayCrtcCtmSupportType" expires_after="M79">
   <owner>afakhry@chromium.org</owner>
   <summary>
     The type of CRTC color transorm matrix support for the currently connected