drm/amd/display: Drop unused code for DCN32/321

Under DCN32/321 we identified some code paths that DC never executes.
This commit removes those unused codes to avoid distractions when
debugging issues.

Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>