Well, actually it's the other way round:
If you use t-code SPNEGO to create a keytab, then SPNego will be activated.
So, if you do not like SPNego to be activated, you must not use t-code SPNEGO to create a keytab.
That's actually independent from the SNC library - in order to be able to use SPNego you have to use a(ny) Kerberos-based SNC library, however (since SPNego and SNC are sharing the same mappings). The t-code SNCWIZARD, however, will only work when using the CommonCryptoLib as SNC library.