Bug 1612449 [wpt PR 21522] - Drop pypy from tox.ini, a=testonly

Automatic update from web-platform-tests
Drop pypy from tox.ini

This has been broken for a while due to https://bitbucket.org/pypy/pypy/issues/3157

--

wpt-commits: 9469d80dc489346bb2f8e71c35ad1d350b4d649d
wpt-pr: 21522

testing/web-platform/tests/tools/tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py27,py35,py36,py37,py38,pypy,{py27,py35,py36,py37,py38}-flake8,{py35,py36,py37,py38}-mypy
+envlist = py27,py35,py36,py37,py38,{py27,py35,py36,py37,py38}-flake8,{py35,py36,py37,py38}-mypy
 skipsdist=True
 skip_missing_interpreters = False