drm: Remove complete task from TODO documentation

This patch remove the follow complete task from TODO documentation:

  drm_mode_config.crtc_idr is misnamed, since it contains all KMS object.
  Should be renamed to drm_mode_config.object_idr.
Signed-off-by: Shayenne da Luz Moura <shayenneluzmoura@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20181213225537.nq4dwidn6tma33iv@smtp.gmail.com

Documentation/gpu/todo.rst

@@ -354,9 +354,6 @@ KMS cleanups
 
 Some of these date from the very introduction of KMS in 2008 ...
 
-- drm_mode_config.crtc_idr is misnamed, since it contains all KMS object. Should
-  be renamed to drm_mode_config.object_idr.
-
 - drm_display_mode doesn't need to be derived from drm_mode_object. That's
   leftovers from older (never merged into upstream) KMS designs where modes
   where set using their ID, including support to add/remove modes.