Remove defunct flushing list (v2)

This is turning into a dinq BUG_ON special. Have fun!
-chris

Follow-Ups:
- [PATCH 13/13] drm/i915: Move the write seqno handling to move_to_active
  - From: Chris Wilson
- [PATCH 12/13] drm/i915: Split i915_gem_flush_ring() into seperate invalidate/flush funcs
  - From: Chris Wilson
- [PATCH 11/13] drm/i915: Clear the pending_gpu_fenced_access flag at the start of execbuffer
  - From: Chris Wilson
- [PATCH 10/13] drm/i915: Replace the complex flushing logic with simple invalidate/flush all
  - From: Chris Wilson
- [PATCH 09/13] drm/i915: Remove the explicit flush of the GPU write domain
  - From: Chris Wilson
- [PATCH 08/13] drm/i915: Remove explicit flush from i915_gem_object_flush_fence()
  - From: Chris Wilson
- [PATCH 07/13] drm/i915: Remove the per-ring write list
  - From: Chris Wilson
- [PATCH 06/13] drm/i915: Remove the defunct flushing list
  - From: Chris Wilson
- [PATCH 05/13] drm/i915: Insert a flush between batches if the breadcrumb was dropped
  - From: Chris Wilson
- [PATCH 04/13] drm/i915: Replace the pending_gpu_write flag with an explicit seqno
  - From: Chris Wilson
- [PATCH 03/13] drm/i915: Allow late allocation of request for i915_add_request()
  - From: Chris Wilson
- [PATCH 02/13] drm/i915: fix invalid reference handling of the default ctx obj
  - From: Chris Wilson
- [PATCH 01/13] drm/i915: Flush the context object from the CPU caches upon creation
  - From: Chris Wilson