docs/devel: fix duplicate line

I guess the same change came in via two patch series. Remove the
repetition.

Fixes: 2a851fca9f (docs/devel: remind developers to run CI container pipeline when updating images)
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240910173900.4154726-5-alex.bennee@linaro.org>

docs/devel/testing/main.rst

@@ -500,12 +500,6 @@ first to contribute the mapping to the ``libvirt-ci`` project:
    `CI <https://www.qemu.org/docs/master/devel/ci.html>`__ documentation
    page on how to trigger gitlab CI pipelines on your change.
 
- * Please also trigger gitlab container generation pipelines on your change
-   for as many OS distros as practical to make sure that there are no
-   obvious breakages when adding the new pre-requisite. Please see
-   `CI <https://www.qemu.org/docs/master/devel/ci.html>`__ documentation
-   page on how to trigger gitlab CI pipelines on your change.
-
 For enterprise distros that default to old, end-of-life versions of the
 Python runtime, QEMU uses a separate set of mappings that work with more
 recent versions.  These can be found in ``tests/lcitool/mappings.yml``.