Remove unused cert code

https://crrev.com/c/2421633 added this file, and originally it had
two policies: one that disabled revocation checking, and one basic
X.509 policy to mimic how SFCertificatePanel behaved with no specified
policies.

The revocation checking policy was removed in
https://crrev.com/c/3657565, but the large comment explaining why it
was there was never removed. Therefore, remove that large comment.

The basic X.509 policy is therefore not needed, because it was only
there to mimic there being no policies, and it's easier to just have
no policies.

Therefore, inline what’s left into its sole caller.

Bug: 327022925
Change-Id: I4af9c52a161aa1bc71dcbf78e7187b462716729f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5332659
Commit-Queue: Avi Drissman <avi@chromium.org>
Auto-Submit: Avi Drissman <avi@chromium.org>
Reviewed-by: David Benjamin <davidben@chromium.org>
Commit-Queue: David Benjamin <davidben@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1266665}