drm/amdgpu/display: remove dal_cmd_tbl_helper_dcn2_get_table2

It's unused and identical to dal_cmd_tbl_helper_dce112_get_table2.

Reviewed-by: Luben Tuikov <luben.tuikov@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>