Extend expiry date for smbfs-file-shares flag

Extending this flag until M90 to give us time to clean up the old
smbprovider code and fully remove flag references.

Bug: 1130910
Change-Id: Id2b0c883bc8334619a8fc36592c473614271ad8d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2423444Reviewed-by: Anand K Mistry <amistry@chromium.org>
Commit-Queue: Josh Simmons <simmonsjosh@google.com>
Cr-Commit-Position: refs/heads/master@{#809233}

chrome/browser/flag-metadata.json

@@ -4163,8 +4163,8 @@
   },
   {
     "name": "smbfs-file-shares",
-    "owners": [ "amistry", "dats" ],
-    "expiry_milestone": 86
+    "owners": [ "simmonsjosh@google.com", "dats" ],
+    "expiry_milestone": 90
   },
   {
     "name": "smooth-scrolling",