drm/i915: Remove unused no-shrinker-steal

After removing the user of this wart, we can remove the wart entirely.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1470388464-28458-10-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_drv.h

@@ -1318,7 +1318,6 @@ struct i915_gem_mm {
 	struct notifier_block oom_notifier;
 	struct notifier_block vmap_notifier;
 	struct shrinker shrinker;
-	bool shrinker_no_lock_stealing;
 
 	/** LRU list of objects with fence regs on them. */
 	struct list_head fence_list;

drivers/gpu/drm/i915/i915_gem_shrinker.c

@@ -244,9 +244,6 @@ static bool i915_gem_shrinker_lock(struct drm_device *dev, bool *unlock)
 		if (!mutex_is_locked_by(&dev->struct_mutex, current))
 			return false;
 
-		if (to_i915(dev)->mm.shrinker_no_lock_stealing)
-			return false;
-
 		*unlock = false;
 	} else
 		*unlock = true;