[Pkg-samba-maint] Old upgrade support

[Peter Eisentraut]

There is a bunch of code in the maintainer scripts for upgrade from 
pre-sarge versions.  Some of this is clearly beginning to rot, as can 
be seen from at least to places to produce exactly the sort of 
invalid "passdb backend" settings that have caused us much pain.

I propose to rip out all code in the maintainer scripts that is within a 
dpkg --compare-versions block that is checking for versions older than 
sarge.