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 <[email protected]>
Reviewed-by: WangYuli <[email protected]>
Signed-off-by: Helen Koike <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: vigneshraman