More cleanup for py2 drop

Change-Id: I064f4f936ad1e63c78db2d5520c4ccd224d77323

requirements.txt

@@ -25,4 +25,4 @@ oslo.utils>=3.36.0 # Apache-2.0
 testtools>=2.2.0 # MIT
 oslotest>=3.2.0 # Apache-2.0
 tempest>=17.1.0 # Apache-2.0
-networkx>=2.3;python_version>='3.4'  # BSD
+networkx>=2.3  # BSD

tox.ini

@@ -18,15 +18,12 @@ deps = -r{toxinidir}/test-requirements.txt
 commands = stestr run {posargs}
 
 [testenv:pep8]
-basepython = python3
 commands = flake8 {posargs}
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [testenv:cover]
-basepython = python3
 setenv =
     VIRTUAL_ENV={envdir}
     PYTHON=coverage run --source virtage_tempest_plugin --parallel-mode
@@ -37,16 +34,13 @@ commands =
     coverage xml -o cover/coverage.xml
 
 [testenv:docs]
-basepython = python3
 commands = python setup.py build_sphinx
 
 [testenv:releasenotes]
-basepython = python3
 commands =
   sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html
 
 [testenv:debug]
-basepython = python3
 commands = oslo_debug_helper {posargs}
 
 [flake8]