drm/drm-kms.rst: Remove unused drm_fourcc.h include directive

Right now there's nothing, and kernel-doc produces a warning because
of that. Remove it until we need it for a clean build.

Cc: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1468612088-9721-1-git-send-email-daniel.vetter@ffwll.ch

Documentation/gpu/drm-kms.rst

@@ -67,9 +67,6 @@ drivers can manually clean up a framebuffer at module unload time with
 DRM Format Handling
 -------------------
 
-.. kernel-doc:: include/drm/drm_fourcc.h
-   :internal:
-
 .. kernel-doc:: drivers/gpu/drm/drm_fourcc.c
    :export: