drm/i915: Remove some dead "code"

Commit 2caffbf1 ("drm/i915: Revoke mmaps and prevent access to fence
registers across reset") removed the temporary implementation of a reset
under stop machine but forgot to remove this one commented out define.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230705095518.3690951-1-tvrtko.ursulin@linux.intel.com