remove the Section member from package struct

remove the Section member from package struct

A version belongs to a section and has hence a section member of its
own. A package on the other hand can have multiple versions from
different sections. This was "solved" by using the section which was
parsed first as order of sources.list defines, but that is obviously a
horribly unpredictable thing.

We therefore directly remove this struct member to free some space and
mark the access method as deprecated, which is told to return the
section of the 'newest' known version, which is at least predictable,
but possible not what it returned before – but nobody knows.

Users are way better of with the Section() as returned by the version
they are dealing with. It is likely the same for all versions of a
package, but in the few cases it isn't, it is important (like packages
moving from main/* to contrib/* or into oldlibs …).