drm/i915: drop unneeded make_unshrinkable in free_object

The comment here is no longer accurate, since the current shrinker code
requires a full ref before touching any objects. Also unset_pages()
should already do the required make_unshrinkable() for us, if needed,
which is also nicely balanced with set_pages().

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211018091055.1998191-4-matthew.auld@intel.com

drivers/gpu/drm/i915/gem/i915_gem_object.c

@@ -363,15 +363,6 @@ static void i915_gem_free_object(struct drm_gem_object *gem_obj)
 	 */
 	atomic_inc(&i915->mm.free_count);
 
-	/*
-	 * This serializes freeing with the shrinker. Since the free
-	 * is delayed, first by RCU then by the workqueue, we want the
-	 * shrinker to be able to free pages of unreferenced objects,
-	 * or else we may oom whilst there are plenty of deferred
-	 * freed objects.
-	 */
-	i915_gem_object_make_unshrinkable(obj);
-
 	/*
 	 * Since we require blocking on struct_mutex to unbind the freed
 	 * object from the GPU before releasing resources back to the