Removing _NetBSD-pkgdb

[Greg Troxel <gdt%lexort.com@localhost>]

After the branch, I intend to rm _NetBSD-pkgdb, a script to recover from
the package database moving.  It's been 4 years and my impression is
that no one needs it any more.  I no longer run into non-migrated
systems, and I don't get questions.  It will of course remain in history
should anyone need it, but it is clutter for up-to-date checkouts.

Speak up if you think this is the wrong path, and explain why the small
minor clutter per person of the script remaining present for all pepple
is outweighed by the benefit of theoretically close to zero people not
having to fish it out of CVS history.  Or some other reason I have it
wrong :-)