drm/amd/display: Remove legacy comments

To improve the code readability, this commit removes a set of commented
and not used functions for a long time. Notice that now we have the
amdgpu_dm_dtn_log, which prints all the relevant information that we
need.

Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Acked-by: Stylon Wang <stylon.wang@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>