Extend PageInfo flag expiry

We still need the flag.

Bug: 1077766
Change-Id: Iba4c5834636845716872209019bd3eb4ccbba5c6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2584925
Auto-Submit: Christian Dullweber <dullweber@chromium.org>
Commit-Queue: Ehimare Okoyomon <eokoyomon@chromium.org>
Reviewed-by: Ehimare Okoyomon <eokoyomon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836545}

chrome/browser/flag-metadata.json

@@ -3832,7 +3832,7 @@
   {
     "name": "page-info-version-2",
     "owners": [ "eokoyomon", "dullweber" ],
-    "expiry_milestone": 88
+    "expiry_milestone": 91
   },
   {
     "name": "paint-preview-demo",