Cleanup tox.ini

Remove old constraint environments, those are not used anywhere.

Note that this repo did not use constraints before and does not use them
now, it's also not part of global requirements process, so we should not
enable it yet.

Fix flake options (even if unused).

Change-Id: I845a4c43eb64d017d1bdf0f428e9e9e39a00c151

tox.ini

@@ -1,28 +1,21 @@
 [tox]
 minversion = 2.0
-envlist = docs,docs-constraints
+envlist = docs
 skipsdist = True
 
 [testenv]
 usedevelop = True
 install_command =
-                  constraints: {[testenv:common-constraints]install_command}
                   pip install -U {opts} {packages}
 setenv =
    VIRTUAL_ENV={envdir}
 deps = -r{toxinidir}/test-requirements.txt
 commands = python setup.py test --slowest --testr-args='{posargs}'
 
-[testenv:common-constraints]
-install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} {opts} {packages}
-
 [testenv:docs]
 commands = python setup.py build_sphinx
 
-[testenv:docs-constraints]
-install_command = {[testenv:common-constraints]install_command}
-commands = python setup.py build_sphinx
-
+[flake8]
 show-source = True
 ignore = E123,E125
 builtins = _