Move AppServiceShelf flag to M82.

BUG=1011235

Change-Id: Ia3d37e3d6943640659dce7df121869222ebee07a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1975387Reviewed-by: Dominick Ng <dominickn@chromium.org>
Commit-Queue: Nancy Wang <nancylingwang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#726285}

chrome/browser/flag-metadata.json

@@ -130,7 +130,7 @@
   {
     "name": "app-service-shelf",
     "owners": [ "//chrome/services/app_service/OWNERS" ],
-    "expiry_milestone": 81
+    "expiry_milestone": 82
   },{
     "name": "arc-application-zoom",
     "owners": [ "sarakato" ],