Remove everything related to the `bt2.ctf_writer` Python module

Remove everything related to the `bt2.ctf_writer` Python module

This module wraps CTF writer, but is currently incomplete and would
require much work to finish, as CTF writer is completely decoupled from
the Babeltrace library.

Since we plan to make Babeltrace 1 and Babeltrace 2 coinstallable, and
that CTF writer 2 does not add many important features to CTF writer 1,
we decided to postpone the development of its Python bindings to when it
supports CTF 2.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: Ie8ceeac8bfcce86dec3cb426d7030ad445274cd2
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1392