tox.ini: remove definitions for deprecated Python versions

Instead of updating them for pytest without testing.

tox.ini

@@ -42,12 +42,6 @@ commands = {envpython} -m pytest \
 basepython = python2.7
 deps = -r{toxinidir}/test-requirements.txt
 
-[testenv:py26]
-deps = -r{toxinidir}/test-requirements.txt
-commands = {envpython} -m pytest {posargs:tests/unittests cloudinit}
-setenv =
-    LC_ALL = C
-
 [flake8]
 #H102  Apache 2.0 license header not found
 ignore=H404,H405,H105,H301,H104,H403,H101,H102,H106,H304
@@ -86,35 +80,6 @@ deps =
     unittest2==1.1.0
     contextlib2==0.5.1
 
-[testenv:centos6]
-basepython = python2.6
-commands = {envpython} -m pytest {posargs:tests/unittests cloudinit}
-deps =
-    # requirements
-    argparse==1.2.1
-    jinja2==2.2.1
-    pyyaml==3.10
-    oauthlib==0.6.0
-    configobj==4.6.0
-    requests==2.6.0
-    jsonpatch==1.2
-    six==1.9.0
-    -r{toxinidir}/test-requirements.txt
-
-[testenv:opensusel150]
-basepython = python2.7
-commands = {envpython} -m pytest {posargs:tests/unittests cloudinit}
-deps =
-    # requirements
-    jinja2==2.10
-    PyYAML==3.12
-    oauthlib==2.0.6
-    configobj==5.0.6
-    requests==2.18.4
-    jsonpatch==1.16
-    six==1.11.0
-    -r{toxinidir}/test-requirements.txt
-
 [testenv:tip-pycodestyle]
 commands = {envpython} -m pycodestyle {posargs:cloudinit/ tests/ tools/}
 deps = pycodestyle