Update flag-metadata.json for allow-sxg-certs-without-extension

Bug: 851778,862003
Change-Id: If6667d8b8f4813748fdd1bceb40850bdfd5da36f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1573431
Commit-Queue: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Kunihiko Sakamoto <ksakamoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652519}
1 file changed