src.ctf.fs: remove ctf_fs_file_destroy

src.ctf.fs: remove ctf_fs_file_destroy

Remove it, and the custom deleter, now that a ctf_fs_file can be simply
deleted.

Change-Id: Iaef8b0cdbe525272019e0258665b45cbaee6ad05
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/8266
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/12304
Tested-by: jenkins <jenkins@lttng.org>