Bug 1366637 - Extend expiration on MEDIA_OGG_LOADED_IS_CHAINED telemetry. r=francois

In order to inform our decision as to when to remove support for
ogg chaining, we should restore the collection of the telemetry
that reports when it's used.

I picked a longer term on the probe, as I expect it will take a
while for usage to drop in the wild.

MozReview-Commit-ID: Kk8kYJw9Opv

--HG--
extra : rebase_source : 419016b31a3321f6956e981c48c07c36f730b500

toolkit/components/telemetry/Histograms.json

@@ -8293,9 +8293,9 @@
   "MEDIA_OGG_LOADED_IS_CHAINED": {
     "record_in_processes": ["main", "content"],
     "alert_emails": ["cpearce@mozilla.com"],
-    "expires_in_version": "53",
+    "expires_in_version": "70",
     "kind": "boolean",
-    "description": "Whether Ogg audio/video encountered are chained or not.",
+    "description": "Whether while playing Ogg audio/video we encountered a chained Ogg. Reported on every audio or video element that loads an Ogg file.",
     "bug_numbers": [1230295]
   },
   "MEDIA_HLS_CANPLAY_REQUESTED": {