drm/komeda: remove unused struct 'gamma_curve_segment'

'gamma_curve_segment' looks like it has never been used.
Remove it.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240516133724.251750-1-linux@treblig.org
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>