Cleanup: src.ctf.lttng-live: rename _is_canceled function

Cleanup: src.ctf.lttng-live: rename _is_canceled function

Rename the `lttng_live_is_canceled()` function to
`lttng_live_graph_is_canceled()` to make it clear it's the graph that
may be canceled and not the lttng_live component.

No behaviour change intended.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Change-Id: I918c5262e4b833eb8ed302eab42df19ceac0cbbc
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1309
Tested-by: jenkins
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>