drm/todo: remove gem_prime_import/export todo

I've done that.
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190614203615.12639-56-daniel.vetter@ffwll.ch

Documentation/gpu/todo.rst

@@ -215,13 +215,6 @@ efficient.
 
 Contact: Daniel Vetter
 
-Defaults for .gem_prime_import and export
------------------------------------------
-
-Most drivers don't need to set drm_driver->gem_prime_import and
-->gem_prime_export now that drm_gem_prime_import() and drm_gem_prime_export()
-are the default.
-
 struct drm_gem_object_funcs
 ---------------------------