drm/amd/display: remove calculate_adjustments in conversion.h

- these are moved to color module

Signed-off-by: Tony Cheng <tony.cheng@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>