Doh, stretch/slim variants are now failing with the following:

	'python-imports' [6/8]...Traceback (most recent call last):
  File "./container.py", line 2, in <module>
    import readline
ImportError: libreadline.so.7: cannot open shared object file: No such file or directory
failed

Kicked off https://travis-ci.org/docker-library/python/builds/296015684 to see if it's introduced by this PR or if it happens in current master 😞

#238 had a totally passing build, so it can't possibly be the fault of that 😞 😱 😕

Oh! gnupg has dep: libreadline7 (>= 6.0), which we were unintentionally keeping, and it's now getting removed properly! 🤘

Will update in a moment.