src.ctf.lttng-live: add lttng_live_session destructor

src.ctf.lttng-live: add lttng_live_session destructor

Convert lttng_live_destroy_session to a destructor.  Add a new
lttng_livelttng_live_destroy_session function that calls delete, it's
still needed for the GPtrArray (which will be removed in a subsequent
patch).

Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Change-Id: Icb2d9c33fb3591e206698b37c9d658ff731184ad
Reviewed-on: https://review.lttng.org/c/babeltrace/+/8466
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>