drm/sched: revert "drm_sched_job_cleanup(): correct false doc"

This reverts commit 44d2f310.

The function drm_sched_job_arm() is indeed the point of no return. The
background is that it is nearly impossible for the driver to correctly
retract the fence and signal it in the order enforced by the dma_fence
framework.

The code in drm_sched_job_cleanup() is for the purpose to cleanup after
the job was armed through drm_sched_job_arm() *and* processed by the
scheduler.

We can certainly improve the documentation, but removing the warning is
clearly not a good idea.

Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Philipp Stanner <phasta@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20250312134400.2176393-1-christian.koenig@amd.com