tox: remove unused environments, add black,isort

All the existing environments were unused and broken. Remove them.
Add black and isort environments to help run a consistent version.

tox.ini

@@ -1,47 +1,18 @@
 [tox]
 envlist =
-    coverage
-    flake8
+    black
+    isort
 recreate = True
 
 [testenv]
 basepython = python3
-setenv =
-    SUBIQUITY_NO_I18N = 1
-    FAKE_TRANSLATE = always
-    PYTHONPATH = {toxinidir}/fake_deps
 
-deps =
-    urwid==1.2.1
-    PyYAML
-    attrs
-    jsonschema
-    pyudev
-    requests
-    requests-unixsocket
+[testenv:black]
+deps = black ~= 23.0
+commands = {envpython} -m black \
+    {posargs:console_conf subiquity subiquitycore system_setup}
 
-[testenv:flake8]
-deps =
-    flake8==3.5.0
-    pycodestyle==2.3.1
-    pyflakes==1.6.0
-
-commands = {envpython} -m flake8 \
-    {posargs:console_conf/ subiquity/ subiquitycore/}
-
-[testenv:py3]
-deps =
-    {[testenv]deps}
-    nose
-commands = {envpython} -m nose \
-    {posargs:console_conf/ subiquity/ subiquitycore/}
-
-[testenv:coverage]
-deps = {[testenv:py3]deps}
-    nose-timer
-    coverage
-commands = {envpython} -m nose \
-    --with-timer --timer-top-n 10 \
-    --with-coverage --cover-erase --cover-branches --cover-inclusive \
-    --cover-package=subiquity --cover-package=subiquitycore \
-    {posargs:console_conf subiquity/ subiquitycore/}
+[testenv:isort]
+deps = isort == 5.12.0
+commands = {envpython} -m isort \
+    {posargs:console_conf subiquity subiquitycore system_setup}