Move expiry of enable-start-surface to M86

Bug: 982018
Change-Id: Ied383279878bcf66eb80343eae34942c06d875b1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2155805Reviewed-by: Ganggui Tang <gogerald@chromium.org>
Commit-Queue: Ganggui Tang <gogerald@chromium.org>
Cr-Commit-Position: refs/heads/master@{#760339}

chrome/browser/flag-metadata.json

@@ -1995,7 +1995,7 @@
   {
     "name": "enable-start-surface",
     "owners": [ "gogerald"],
-    "expiry_milestone": 83
+    "expiry_milestone": 86
   },
   {
     "name": "enable-storage-pressure-ui",