cli: remove unused path variable in set_stream_intersections

cli: remove unused path variable in set_stream_intersections

The `path` variable is used in the error message, but never set, so it
will always appear as "(unknown)".

In the future, it would be nice if the error message gave more info to
the user.  But right now, it is pointless to keep `path` there, so
remove it.

Change-Id: If55d8246dde8cffe1b584477643f105acaaa4792
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1992
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Francis Deslauriers <francis.deslauriers@efficios.com>