drm/amd/display: Revert "drm/amd/display: turn DPMS off on connector unplug"

This reverts commit 3c4d55c9.

Revert the commit because:
- It's incomplete of the function dm_set_dpms_off() for mst case.  For
  stream sinks whithin the same mst topology, they share the same dc_link.
  dm_set_dpms_off() tries to update one mst stream only which is
  incomplete.
- Setting dpms off should be triggered by usermode. Besdies, it seems
  usermode does release relevant resource for mst & non-mst case when
  unplug connecotr now.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Aurabindo Jayamohanan Pillai <Aurabindo.Pillai@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Acked-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>