drm/i915: Kill private_default_ctx off

It's barely alive now anyway, so give it the "coup de grâce".

Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -1780,7 +1780,6 @@ struct drm_i915_file_private {
 	} mm;
 	struct idr context_idr;
 
-	struct intel_context *private_default_ctx;
 	atomic_t rps_wait_boost;
 	struct  intel_engine_cs *bsd_ring;
 };