third_party/cloud_authenticator: stop using bssl-sys

The use of bssl-sys was temporary while bssl-crypto was reworked. Now
that's complete, switch to using bssl-crypto.

Change-Id: I41fdab3fd75ffb2ae1286b64d03294477b292066
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5218424
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Commit-Queue: Adam Langley <agl@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1252945}
NOKEYCHECK=True
GitOrigin-RevId: b19d31ced2bab4f1176322f3044890fa0f00c20f
1 file changed