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

drivers/gpu/drm/i915/gt/intel_reset.c

@@ -34,9 +34,6 @@
 
 #define RESET_MAX_RETRIES 3
 
-/* XXX How to handle concurrent GGTT updates using tiling registers? */
-#define RESET_UNDER_STOP_MACHINE 0
-
 static void client_mark_guilty(struct i915_gem_context *ctx, bool banned)
 {
 	struct drm_i915_file_private *file_priv = ctx->file_priv;