drm/ci: remove update-xfails.py

We can remove the xfails/update-xfails.py script as it is not
used in CI jobs. Once ci-collate [1] is tested for drm-ci,
we can use this tool directly to update fails and flakes.

[1] https://gitlab.freedesktop.org/gfx-ci/ci-collate/



Signed-off-by: Vignesh Raman <vignesh.raman@collabora.com>
Reviewed-by: WangYuli <wangyuli@uniontech.com>
Signed-off-by: Helen Koike <helen.koike@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241030091732.665428-1-vignesh.raman@collabora.com