Cleanup docs building

a few cleanups:
- Remove obsolete sections from setup.cfg
- Switch to using sphinx-build
- Remove install_command from tox.ini, the default is fine

Change-Id: Id706786bed4b20682704d524986850b7c71e225d

setup.cfg

@@ -11,14 +11,3 @@ classifier =
     Intended Audience :: Developers
     License :: OSI Approved :: Apache Software License
     Operating System :: POSIX :: Linux
-
-[build_sphinx]
-source-dir = doc/source
-build-dir = doc/build
-all_files = 1
-
-[pbr]
-warnerrors = True
-
-[upload_sphinx]
-upload-dir = doc/build/html

tox.ini

@@ -6,7 +6,6 @@ skipsdist = True
 [testenv]
 basepython = python3
 usedevelop = True
-install_command = pip install -U {opts} {packages}
 setenv =
    VIRTUAL_ENV={envdir}
 deps = -r{toxinidir}/requirements.txt
@@ -20,7 +19,7 @@ commands =
 commands = {posargs}
 
 [testenv:docs]
-commands = python setup.py build_sphinx
+commands = sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:spelling]
 deps =