drm/i915/skl: revert duplicated WaBarrierPerformanceFixDisable:skl

With this simple git diff command one can see that skl_init_workarounds()
got two copies of WaBarrierPerformanceFixDisable:skl:

 git diff -U21 ca6e4405^1 ca6e4405 drivers/gpu/drm/i915/intel_ringbuffer.c

This happened when the backmerge of drm-intel-fixes-2015-07-15
Merged the same fix on both sides. Same fix but not identical enough for
git: with a different surrounding context; hence the code duplication.

This commit merely reverts the output of the git command above
 = the duplication introduced in the backmerge.

(This duplication was found while running git sanity checks on a
_linearized_ i915 forklift for ChromeOS.)
Signed-off-by: Marc Herbert <marc.herbert@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -1041,13 +1041,6 @@ static int skl_init_workarounds(struct intel_engine_cs *ring)
 		WA_SET_BIT_MASKED(HIZ_CHICKEN,
 				  BDW_HIZ_POWER_COMPILER_CLOCK_GATING_DISABLE);
 
-	if (INTEL_REVID(dev) == SKL_REVID_C0 ||
-	    INTEL_REVID(dev) == SKL_REVID_D0)
-		/* WaBarrierPerformanceFixDisable:skl */
-		WA_SET_BIT_MASKED(HDC_CHICKEN0,
-				  HDC_FENCE_DEST_SLM_DISABLE |
-				  HDC_BARRIER_PERFORMANCE_DISABLE);
-
 	if (INTEL_REVID(dev) <= SKL_REVID_D0) {
 		/*
 		 *Use Force Non-Coherent whenever executing a 3D context. This