drm/amd/display: remove an unused file

[Why&How]
Internal subvp state is not referenced in driver code, so it can be removed.

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