amdgpu/dc: drop dml display_mode_support.c (v2)

This code isn't used, and this function is huge, reimport later if
going to be used.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>