Remove popt from project's dependencies

Remove popt from project's dependencies

All of the argument parsing having been moved to use the internal argpar
library, we can now stop linking with popt.  And since it was the last
use of popt in the repo, remove anything related to it.

Change-Id: Id2aee4869780e586833d6b6646e12e19c6d78f6a
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1795
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>