Win7 and Server 2003 are already irrelevant now, and will be absurdly so by the time Pg 9.6 comes out.
The windows feature works better than the in-application crash dump. It can limit the number of dumps, for one thing, and it doesn't require a sane and intact stack to work.
Even if it's all good in recent Windows, the impression I have is that an awful lot of people are still running older versions, so I'd be pretty hesitant to just drop the code.
Yeah, if it was new in Win2012 I'd agree, but it's been around since 2008.
Also, AFAICS it's pretty self-contained and hence not much of a drag on development. Is there any positive reason to remove it?
Not really. It also does nothing by default, so it's pretty harmless and mostly dead code.
I just thought it was worth bringing up that there's a better way to do it now and nobody seems to use it anyway.