generate_configurations.py was removed in the tox rewrite. (#420)

Cf [tox + travis-ci changes](#390)

Author: jmccarrell

docs/contributing.rst

@@ -142,10 +142,6 @@ flag::
 This will run the tests on Python 3.3/Django 1.7/PostgeSQL and Python
 2.7/Django 1.9/SQLite.
 
-The tox and Travis CI configuration is generated by the script
-`generate_configurations.py` in the root directory. To add tests for a new
-Python or Django version, simply update the script and run it to regenerate the
-configuration files.
 
 Measuring test coverage
 -----------------------