drm/tests: Drop drm_kunit_helper_acquire_ctx_alloc()

drm/tests: Drop drm_kunit_helper_acquire_ctx_alloc()

lockdep complains when a lock is released in a separate thread the
lock is taken in, and it turns out that kunit does run its actions in a
separate thread than the test ran in.

This means that drm_kunit_helper_acquire_ctx_alloc() just cannot work as
it's supposed to, so let's just get rid of it.

Suggested-by: Simona Vetter <simona.vetter@ffwll.ch>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20250220132537.2834168-1-mripard@kernel.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>