drm/amd/amdgpu_dm/mst: Remove useless sideband tracing

We already trace DPCD reads/writes on both MST and SST, there's no
reason to have this code here (plus, toggling these things with a
define at the top of the file isn't how we do things in the kernel).

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>