drm/i915: remove unused orig_clock i915 member

Unused since commit f97108d1 ("drm/i915: add dynamic performance
control support for Ironlake"). That's a little over ten years. Good
riddance.
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200227170047.31089-2-jani.nikula@intel.com

drivers/gpu/drm/i915/i915_drv.h

@@ -1048,8 +1048,6 @@ struct drm_i915_private {
 		struct work_struct free_work;
 	} atomic_helper;
 
-	u16 orig_clock;
-
 	bool mchbar_need_disable;
 
 	struct intel_l3_parity l3_parity;