removing global_schemacheck and SLAPD_LASTMOD flags

["Kurt D. Zeilenga" <Kurt@OpenLDAP.org>]

These flags should always be TRUE.  If FALSE, slapd(8)
will likely not behave correctly (especially in the
case of global_schemacheck).

I am about to add some manage DIT capabilities and
rather not have to deal with the possibility that
these flags are FALSE.  Hence, I propose axing
these flags.  Comments?

Kurt