kernel/codeset: Make CodeSet's memory data member a regular std::vector

The use of a shared_ptr is an implementation detail of the VMManager
itself when mapping memory. Because of that, we shouldn't require all
users of the CodeSet to have to allocate the shared_ptr ahead of time.
It's intended that CodeSet simply pass in the required direct data, and
that the memory manager takes care of it from that point on.

This means we just do the shared pointer allocation in a single place,
when loading modules, as opposed to in each loader.