[omnibox] Extend the expiry milestone to M82 for on device head

suggestions.

Bug: 925072
Change-Id: Ia22128991b70a5ce69f48ab2eb89c20e6af10b8f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1918119
Commit-Queue: Ce Chen <cch@chromium.org>
Reviewed-by: Tommy Li <tommycli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715498}

chrome/browser/flag-metadata.json

@@ -2809,7 +2809,7 @@
   {
     "name": "omnibox-on-device-head-suggestions",
     "owners": [ "cechen", "suggest-2g@google.com" ],
-    "expiry_milestone": 80
+    "expiry_milestone": 85
   },
   {
     "name": "omnibox-on-focus-suggestions",