drm/exynos: remove leftover functions declarations

These functions were already removed by previous cleanup work, but these
ones were left behind.
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Acked-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_crtc.h

@@ -28,12 +28,6 @@ void exynos_drm_crtc_disable_vblank(struct drm_device *dev, int pipe);
 void exynos_drm_crtc_finish_pageflip(struct drm_device *dev, int pipe);
 void exynos_drm_crtc_complete_scanout(struct drm_framebuffer *fb);
 
-void exynos_drm_crtc_plane_mode_set(struct drm_crtc *crtc,
-			struct exynos_drm_plane *plane);
-void exynos_drm_crtc_plane_commit(struct drm_crtc *crtc, int zpos);
-void exynos_drm_crtc_plane_enable(struct drm_crtc *crtc, int zpos);
-void exynos_drm_crtc_plane_disable(struct drm_crtc *crtc, int zpos);
-
 /* This function gets pipe value to crtc device matched with out_type. */
 int exynos_drm_crtc_get_pipe_from_type(struct drm_device *drm_dev,
 					unsigned int out_type);