Revert "ps: extend the non-standard option -d (tree view) to work with -p"

This reverts commit ca8c0d5e811048ad67d0955642c5b486e9c0f3d2.

By commiting ca8c0d5e8110 I was hoping that the existing option -d
could just be extended to work with -p to implement a feature that was
and I think is still needed, that is to show all descendant processes
of a given process id or a set of process ids.

After a complaint from -current which may represent a wider
dissatisfaction with this change in the program's behavior, I think it
will be better to revert ca8c0d5e8110 and reintroduce this feature
using a separate option -D.