Do not check revocation status of leaf certificate

The leaf certificate is generated at runtime and contains attestation
attributes specific to this attestation operation instance, including
the one-time challenge. This certificate is ephemeral and will not be
revoked.

Test: manually
Bug: 389088384
Flag: EXEMPT bug fix
Change-Id: I614f0ed18fe1154b089f6ecdada6c458fd545e53