src.ctf.fs: remove ctf_fs_ds_index_entry_create

src.ctf.fs: remove ctf_fs_ds_index_entry_create

This function is now a simple wrapper around constructing a
ctf_fs_ds_index_entry, remove it.

Change-Id: I20905864876588f7e6db79b6b344833275131871
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/8347
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/12342
Tested-by: jenkins <jenkins@lttng.org>