drm/amd/display: remove a function that does complex calculation in every frame but not used

[why]
The result of predict_pipe_split calculation is no longer used but the
function is not removed. This will cause unnecessary calculation
of pipe split prediction in every frame update.

Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Acked-by: Stylon Wang <stylon.wang@amd.com>
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>