Don't bother keeping up with MOK issuers and serial numbers.

Don't bother keeping up with MOK issuers and serial numbers.

* csclient.cxx: Instead of keeping up with MOK issuer, serial number, and
  fingerprints, just handle fingerprints.
* stap-serverd.cxx: Ditto.
* nsscommon.cxx (read_cert_info_from_file): Only return the cert's
  fingerprint.
* nsscommon.h: Update read_cert_info_from_file() prototype.
* session.h: Rename 'mok_info' to 'mok_fingerprints'.
* session.cxx (systemtap_session): Ditto.
* buildrun.cxx (make_run_command): Ditto.