drm/amd/display: Remove drm_dsc_dc.c

This file was accidentally added to the driver during
Navi promotion

Nothing includes it. No makefile attempts to compile it, and
it would fail compilation if they tried

Remove it
Signed-off-by: David Francis <David.Francis@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>w
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>