Remove build files & apparent test data, and update setup.py in place,
all as promised in commit 32df12393eae3f1ce8c00ac99d07e4045a3fbda6.

In theory, the result is the pristine OpenSTV-1.7 release.  See commit
20c31b1cd55a73e62e2111145d33afa517fcc96b for the full story.