bug#26180: Remove motif toolkit support

[Glenn Morris]

martin rudalics wrote:

> As a matter of fact, the only person affected by such a change in the
> positive sense could be me: I'd have one build less to care about.

If you are really saying that only you would benefit from this
simplification (?), then I disagree with you.

> Still, it's sometimes reassuring when both Lucid and Motif handle a
> strange case the same way.

If this is the best (so far the only?) reason to keep Motif,
then it's pretty weak, IMO.