Remove pypy tests

Would love to support pypy, but the tests
don't currently pass.  I suspect I'll need
to avoid ctypes and use a pure python strtod
implementation.

tox.ini

@@ -1,10 +1,5 @@
-# Tox (http://codespeak.net/~hpk/tox/) is a tool for running tests
-# in multiple virtualenvs. This configuration file will run the
-# test suite on all supported python versions. To use it, "pip install tox"
-# and then run "tox" from this directory.
-
 [tox]
-envlist = py26, py27, pypy
+envlist = py26, py27
 
 [testenv]
 commands = nosetests -v