Test fixtures have dramatically increased the size of the release tarball

This bug was originally reported by Chris Lamb (lamby@debian.org) in Debian bug #894334:

Hi,

Since diffoscope 89, the release tarball has got a bit bigger:

  diffoscope-88.tar.bz2  04-Nov-2017 15:38   828K
  diffoscope-89.tar.bz2  25-Dec-2017 14:40   8.9M

The date of the "89" release might suggest some Saturnalian self-
indulgence, but I believe this is actually due to:

  $ ls -lh tests/data/android*.img
  -rw-r--r-- 1 lamby lamby 4.1M 2018-03-29 10:01 tests/data/android1.img
  -rw-r--r-- 1 lamby lamby 4.1M 2018-03-29 10:01 tests/data/android2.img