drm/i915: Remove leftover gem.pm_notifier member

Since we removed the pm hookup from the GT, the hook in
drm_i915_private.gem is unused. Remove it.

References: 18f3b272 ("drm/i915: Remove pm park/unpark notifications")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191112113434.31088-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_drv.h

@@ -1252,8 +1252,6 @@ struct drm_i915_private {
 	struct intel_gt gt;
 
 	struct {
-		struct notifier_block pm_notifier;
-
 		struct i915_gem_contexts {
 			spinlock_t lock; /* locks list */
 			struct list_head list;