Kill unused fence pipelining

Since we have never succeeded in making the pipelined fence updates
stable and it appears we never will, delete the dead code.
-Chris

Follow-Ups:
- [PATCH 12/12] drm/i915: Only the zap the VMA after updating the tiling parameters
  - From: Chris Wilson
- [PATCH 11/12] drm/i915: Clarify the semantics of tiling-changed by renaming it
  - From: Chris Wilson
- [PATCH 10/12] drm/i915: Refactor get_fence() to use the common fence writing routine
  - From: Chris Wilson
- [PATCH 09/12] drm/i915: Refactor fence clearing to use the common fence writing routine
  - From: Chris Wilson
- [PATCH 08/12] drm/i915: Refactor put_fence() to use the common fence writing routine
  - From: Chris Wilson
- [PATCH 07/12] drm/i915: Prepare to consolidate fence writing
  - From: Chris Wilson
- [PATCH 06/12] drm/i915: Remove the unsightly "optimisation" from flush_fence()
  - From: Chris Wilson
- [PATCH 05/12] drm/i915: Simplify fence finding
  - From: Chris Wilson
- [PATCH 04/12] drm/i915: Discard the unused obj->last_fenced_ring
  - From: Chris Wilson
- [PATCH 03/12] drm/i915: Remove unused ring->setup_seqno
  - From: Chris Wilson
- [PATCH 02/12] drm/i915: Remove fence pipelining
  - From: Chris Wilson
- [PATCH 01/12] drm/i915: Remove the pipelined parameter from get_fence()
  - From: Chris Wilson