remove inventory based testing

The inventory based testing for create-diff-object was introduced at a
time when create-diff-object only needed the two object files to operate.
Now, it requires vmlinux as well.  This makes the inventory testing (a
unit testing framework for create-diff-object) obsolete and difficult to
update in its current form.

This commit removes the inventory test framework.

Signed-off-by: Seth Jennings <sjenning@redhat.com>