setup: Move test dependencies into tox configuration.

pytest-runner, and generally doing this through setuptools, is deprecated.
A little sad, but understandable. Handle tests in tox as recommended.

CODE.rst

@@ -14,4 +14,4 @@ The ``paypal-query`` tool is implemented in ``cliquery.py``. Other submodules li
 Running tests
 -------------
 
-Run ``./setup.py test`` to run unit tests. Run ``./setup.py typecheck`` to run the type checker. Run ``tox`` to run both on all supported Pythons.
+Run ``pytest`` to run unit tests. Run ``mypy paypal_rest`` to run the type checker. Run ``tox`` to run both on all supported Pythons.

setup.cfg

@@ -13,10 +13,6 @@ project_urls =
   Source = %(url)s
 url = https://k.sfconservancy.org/NPO-Accounting/paypal_rest
 
-[aliases]
-test=pytest
-typecheck=pytest --addopts="--mypy paypal_rest"
-
 [bdist_wheel]
 universal = 1
 
@@ -42,10 +38,6 @@ install_requires =
   requests-oauthlib>=1.0
 packages = find:
 python_requires = >=3.6
-tests_require =
-  mypy>=0.770
-  pytest
-  pytest-runner
 
 [options.entry_points]
 console_scripts =
@@ -56,9 +48,14 @@ exclude =
   tests
 
 [testenv]
+deps =
+  mypy>=0.770
+  pytest>=3.0
+  pytest-mypy
+
 commands =
-  ./setup.py test
-  ./setup.py typecheck
+  pytest
+  pytest --mypy paypal_rest
 
 [tool:pytest]
 filterwarnings =