Use argpar from upstream

Use argpar from upstream

Now that argpar is maintained in a separate repository, sync the code
with it and remove tests from this code base.

The code was sync'ed  with the argpar repository at commit:

    f46b510674785c70781a3de06c02888faded5db9 (HEAD -> master,
    Strip trailing spaces

Change-Id: Ie805db224f2d3890decbed26a1c80c105d083293
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/2616