Move back to openssl::X509 in tests

Commit fbf77448d57e8f02ba8d ("Keystore VTS for module hash") in
aosp/3426555 changed the X.509 library used for checking serial number
and subject. However, this change inadvertently made the test stricter
(requiring that the implementation use a specific ASN.1 string type).

So revert back to the previous code.

Bug: 395492964
Test: keystore2_client_tests
Change-Id: Icce5a31cd1306fa3ea08896d8440e2888fa5dfed
1 file changed