[Extensions UI] Un-expire the ExtensionsToolbarMenu flag

We still need it around. Extend it through M87.

Bug: 1085244
Change-Id: I61c18a1968687d4cf822ea8f8fcd684a98bf6340
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2210447Reviewed-by: Collin Baker <collinbaker@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#770874}

chrome/browser/flag-metadata.json

@@ -2484,7 +2484,7 @@
   {
     "name": "extensions-toolbar-menu",
     "owners": [ "//extensions/OWNERS", "pbos" ],
-    "expiry_milestone": 84
+    "expiry_milestone": 87
   },
   {
     "name": "file-handling-api",