src.ctf.fs: remove ctf_fs_ds_index_create

src.ctf.fs: remove ctf_fs_ds_index_create

Remove ctf_fs_ds_index_create, since it's now just a wrapper around
constructing a ctf_fs_ds_index.

Change-Id: Ia256fde3286f3f77a514835806f8862678e02359
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/8308
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/12335
Tested-by: jenkins <jenkins@lttng.org>