Extend kIntentPicker flag expiry milestone to M80.

The intent picker for all desktop platforms is launched in M77, so
extend the expiry milestone to M80.

BUG=None

Change-Id: I6f5c057237273b3415866d3d959e50f1dd571c7c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1858027Reviewed-by: Melissa Zhang <melzhang@google.com>
Commit-Queue: Maggie Cai <mxcai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#705804}

chrome/browser/flag-metadata.json

@@ -1380,7 +1380,7 @@
   {
     "name": "enable-intent-picker",
     "owners": [ "chromeos-apps-foundation-team@google.com" ],
-    "expiry_milestone": 78
+    "expiry_milestone": 80
   },
   {
     "name": "enable-javascript-harmony",