Merge pull request #632 from plone/req

Remove sphinx requirements.

requirements.txt

@@ -1,29 +1,3 @@
 # https://github.com/plone/buildout.coredev/blob/5.1/requirements.txt
 setuptools==40.4.3
 zc.buildout==2.12.2
-# Sphinx / ReadTheDocs
-alabaster==0.7.10
-appdirs==1.4.2
-astunparse==1.5.0
-Babel==2.5.1
-certifi==2017.11.5
-chardet==3.0.4
-docutils==0.14
-idna==2.6
-imagesize==0.7.1
-Jinja2==2.10
-MarkupSafe==1.0
-packaging==16.8
-Pygments==2.2.0
-pyparsing==2.1.10
-pytz==2017.3
-requests==2.20.0
-six==1.10.0
-snowballstemmer==1.2.1
-Sphinx==1.6.5
-sphinx-rtd-theme==0.2.4
-sphinxcontrib-httpdomain==1.5.0
-sphinxcontrib-httpexample==0.9.1
-sphinxcontrib-websupport==1.0.1
-typing==3.6.2
-urllib3==1.22