drm/i915: remove unused macro I915_GTT_OFFSET_NONE

Apparently the last user of the macro was removed in commit 9c4ce97d
("drm/i915/display: Be explicit in handling the preallocated vma").
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/b28b183457cf8871b1b070cbbbc3473bd5288210.1662390010.git.jani.nikula@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -459,8 +459,6 @@ static inline struct intel_gt *to_gt(struct drm_i915_private *i915)
 	     (engine__) && (engine__)->uabi_class == (class__); \
 	     (engine__) = rb_to_uabi_engine(rb_next(&(engine__)->uabi_node)))
 
-#define I915_GTT_OFFSET_NONE ((u32)-1)
-
 #define INTEL_INFO(dev_priv)	(&(dev_priv)->__info)
 #define RUNTIME_INFO(dev_priv)	(&(dev_priv)->__runtime)
 #define DRIVER_CAPS(dev_priv)	(&(dev_priv)->caps)