krb5_gss_inquire_cred_by_mech checks its mech argument against two of
the four mechs a krb5 cred might have (the krb5 mech and the old krb5
mech, but not the wrong Microsoft mech or the IAKERB mech), so would
spuriously fail for the other two mechs. There is no reason to check
the mechanism if we assume a reasonable mechglue is interpreting
application gss_inquire_cred_by_mech calls, so just remove the check.
Commit By: ghudson