bug#306: build problem w/ 22 branch: double DOC files

[David Reitter]

I've been getting two identical DOC files (DOC-22.2.50.1,  
DOC-22.2.50.2) with the 22 branch builds on a Carbon machine, using

mac/make-package --self-contained --build-in-place

A log file is available here: 
http://plume.sr.unh.edu/~reitter/Aquamacs/latest-logs/emacs-build.log
(this is updated twice a day).

Given that the files are rather large, I don't think we should keep  
two of them around.

I also noticed that the files accumulate when doing several  
incremental --build-in-place builds, which isn't great either.