src.ctf.fs: change a pointer parameter to a reference, remove unused parameter

src.ctf.fs: change a pointer parameter to a reference, remove unused parameter

 - Change add_range's range parameter to a const ref.
 - Remove the output parameter of populate_stream_info, its caller
   doesn't use it.

Change-Id: I9d9268b3f3e6f6446b2422e9bfb098359c71da02
Reviewed-on: https://review.lttng.org/c/babeltrace/+/8425
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/12359
CI-Build: Simon Marchi <simon.marchi@efficios.com>
Tested-by: jenkins <jenkins@lttng.org>