tests: Remove 'tests/run.py'

This is no longer necessary. One test needs to be modified to deal with
how 'python -m pytest' modifies the PATH.

Signed-off-by: Stephen Finucane <stephen@that.guru>

tox.ini

@@ -22,7 +22,7 @@ deps =
 setenv =
     SPHINX_TEST_TEMPDIR = {envdir}/testbuild
 commands=
-    {envpython} -Wall tests/run.py --durations 25 {posargs}
+    pytest -Wall --durations 25 {posargs}
 
 [testenv:flake8]
 description =