cli: remove the global volatile `interrupted` variable

We can use the global interrupter's state instead, and we don't need to
check the interruption status before calling bt_query_executor_query()
and bt_graph_run() as both functions check their interruption state
initially.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: I3818843c44b016cf2b872d879b461eae52730e6b
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1758
Tested-by: jenkins <jenkins@lttng.org>