[Checkins] [zopefoundation/zope.interface] 1de555: Remove deprecated use of setuptools features

[Marius Gedminas]

  Branch: refs/heads/remove-deprecated-setuptools-feature
  Home:   https://github.com/zopefoundation/zope.interface
  Commit: 1de55506a33bedeb25051ac4cfa18f2e241a9212
      https://github.com/zopefoundation/zope.interface/commit/1de55506a33bedeb25051ac4cfa18f2e241a9212
  Author: Marius Gedminas <marius at gedmin.as>
  Date:   2020-01-20 (Mon, 20 Jan 2020)

  Changed paths:
    M setup.py

  Log Message:
  -----------
  Remove deprecated use of setuptools features

The feature was used to optionally disable C extension modules used for
speed optimizations.

Nowadays we can disable this extension module by setting the PURE_PYTHON
environment variable.

Closes #30.