core: remove Unassigned_64 from osinfo

Unassigned_64 was introduced to be the base of 64 bit definitions but
its not in use and should be removed.

Bug-Url: https://bugzilla.redhat.com/980813

Change-Id: I40fe09bd352a8de932d3999434936c75ad53ebf7
Signed-off-by: Roy Golan <rgolan@redhat.com>