Re: NR pdf is larger with current git by 15%

[Masamichi Hosoda]

>> `selectdevice` does `setdevice` and then `.setdefaultscreen`.
>> If we use only `setdevice`, then `.setdefaultscreen` is not done.
> 
> Aha. So should we just call .setdefaultscreen ourselves? (calling
> "[...] setdevice (pdfwrite) finddevice setdevice" is duplicate) Looks
> like it was introduced long ago, so we can safely rely on it.

It seems that `.setdefaultscreen` is not described
at current Ghostscript documents.
Ghostscript sometimes removes old or undocumented features,
so it's better not to use them in my humble opinion.
e.g. https://ghostscript.com/pipermail/gs-devel/2020-May/010295.html

To avoid duplicate `setdevice`, we can do the following.

```
mark [...snip...] (pdfwrite) finddevice putdeviceprops pop (pdfwrite) 
selectdevice
```

I've created merge request !242.