drm/amd/display: Remove MPC gamut remap logic for DCN30

[Why?]
Should only reroute gamut remap to mpc unless 3D LUT is not used and all
planes are using the same src->dest.

[How?]
Remove DCN30 specific logic for rerouting gamut remap to mpc.

Bug: drm/amd#1513


Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Dillon Varone <dillon.varone@amd.com>
Reviewed-by: Krunoslav Kovac <Krunoslav.Kovac@amd.com>
Acked-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Solomon Chiu <solomon.chiu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org