Fix webpki tests after update

[est31]

If you check out c0344db you will see the tests succeed. But if you check out master after the webpki update in adde38f, you will see that there are deprecation warnings, which we disabled in 3a18b55. There is also a test failure now:

---- test_webpki_crl_parse stdout ----
thread 'test_webpki_crl_parse' panicked at 'failed to find expected revoked cert in CRL', tests/webpki.rs:456:10
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

This needs to be investigated and fixed