Unexpire CECPQ2 feature flag.

I plan on continuing the rollout of this in 2021, really.

BUG=930812

Change-Id: I8e7f3128ec143439428fda340a58bec151204ce1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2595920
Commit-Queue: Adam Langley <agl@chromium.org>
Commit-Queue: David Benjamin <davidben@chromium.org>
Auto-Submit: Adam Langley <agl@chromium.org>
Reviewed-by: David Benjamin <davidben@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837761}

chrome/browser/flag-metadata.json

@@ -3965,7 +3965,7 @@
   {
     "name": "post-quantum-cecpq2",
     "owners": [ "agl" ],
-    "expiry_milestone": 86
+    "expiry_milestone": 100
   },
   {
     "name": "prefetch-notification-scheduling-integration",