Revert "fix tox python3 overrides"

This reverts commit 51a4ccab70.

Change-Id: I52b3ff4699f6907cb481f016fb55fb9102c48b98
Signed-off-by: Thanh Ha <zxiiro@linux.org>

tox.ini

@@ -24,7 +24,6 @@ whitelist_externals =
     find
 
 [testenv:tips]
-basepython = python3
 # tests what happens with unreleased version of dependencies, like python-jenkins
 install_command = pip install -U {opts} {packages}
 commands =
@@ -34,7 +33,6 @@ commands =
     stestr run --slowest {posargs}
 
 [testenv:cover]
-basepython = python3
 setenv =
     {[testenv]setenv}
     PYTHON=coverage run --source jenkins_jobs --parallel-mode
@@ -49,35 +47,28 @@ basepython = python3
 commands = flake8
 
 [testenv:pyflakes]
-basepython = python3
 deps = pyflakes
 commands = pyflakes jenkins_jobs tests setup.py
 
 [testenv:compare-xml-config]
-basepython = python3
 commands = jenkins-jobs {posargs:test -o .test/run-conf/default/out/ .test/run-conf/config/}
 
 [testenv:compare-xml-old]
-basepython = python3
 commands = jenkins-jobs test -o .test/old/out/ .test/old/config/
 
 [testenv:compare-xml-new]
-basepython = python3
 commands = jenkins-jobs test -o .test/new/out/ .test/new/config/
 
 [testenv:docs]
-basepython = python3
 commands = python setup.py build_sphinx {posargs}
 
 [testenv:docs-linkcheck]
-basepython = python3
 # If you are behind a proxy, for this test to work you will need to set
 # TOX_TESTENV_PASSENV="http_proxy https_proxy no_proxy ..." to pass
 # through the proxy environment settings to be able to validate any urls.
 commands = python setup.py build_sphinx -b linkcheck
 
 [testenv:venv]
-basepython = python3
 commands = {posargs}
 
 [flake8]