tests: remove test_ctf_writer_clock.py

tests: remove test_ctf_writer_clock.py

Commit 0fd756a43bce605875565a14c1ed1b070fa3ad94 ("Remove everything
related to the `bt2.ctf_writer` Python module") removed the Python
bindings for the CTF writer.

A corresponding test is still there, but skipped.  I think it can be
removed as well.

Change-Id: I04091a0bc3f04a87c01947956108d83006d9330b
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/2204
Reviewed-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Tested-by: jenkins <jenkins@lttng.org>