Fix: lttng_destroy_session_no_wait: return 0 on success

Fix: lttng_destroy_session_no_wait: return 0 on success

lttng_destroy_session_no_wait() is supposed to behave like
lttng_destroy_session():

> Return 0 on success else a negative LTTNg error code.

However, it returns LTTNG_OK on success. Make it return 0 instead.

Signed-off-by: Christophe Bedard <christophe.bedard@apex.ai>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I787307d4291babfb9ddcb12937efdbfbb5fd7009