Update Sphinx and modules versions

- Only build branches, not every point release
- Bump site copyright date
- Remove a few unused sphinx extensions

Change-Id: I96468446f1f85fdff2daf5a9e1e7e8b85b61b378
diff --git a/conf.py b/conf.py
index b40278b..05a442a 100644
--- a/conf.py
+++ b/conf.py
@@ -25,7 +25,7 @@
 # -- Project information -----------------------------------------------------
 
 project = u'VOLTHA Docs'
-copyright = u'2019-2020, VOLTHA Contributors & Open Networking Foundation'
+copyright = u'2019-2021, VOLTHA Contributors & Open Networking Foundation'
 author = u'VOLTHA Contributors'
 
 # The short X.Y version
@@ -53,18 +53,9 @@
     'sphinx.ext.ifconfig',
     'sphinx.ext.mathjax',
     'sphinx.ext.todo',
-    'sphinxcontrib.actdiag',
-    'sphinxcontrib.blockdiag',
-    'sphinxcontrib.nwdiag',
-    'sphinxcontrib.openapi',
-    'sphinxcontrib.packetdiag',
-    'sphinxcontrib.rackdiag',
-    'sphinxcontrib.seqdiag',
     'sphinxcontrib.spelling',
     "sphinx_multiversion",
     "sphinx.ext.intersphinx",
-#    'sphinxcontrib.golangdomain',
-#    'autoapi.extension',
 ]
 
 # API documentation
@@ -88,6 +79,9 @@
     'make prep',
 ]
 
+# don't include tags
+smv_tag_whitelist = None
+
 # inlcude only the branches matching master and voltha-*
 smv_branch_whitelist = r'^(master|voltha-.*)$'
 
diff --git a/readme.rst b/readme.rst
index 6beac1d..37dce15 100644
--- a/readme.rst
+++ b/readme.rst
@@ -56,17 +56,3 @@
 `Graphviz
 <https://www.sphinx-doc.org/en/master/usage/extensions/graphviz.html>`_
 supports many standard graph types.
-
-The `blockdiag <http://blockdiag.com/en/blockdiag/sphinxcontrib.html>`_,
-`nwdiag, and rackdiag <http://blockdiag.com/en/nwdiag/sphinxcontrib.html>`_,
-and `seqdiag <http://blockdiag.com/en/seqdiag/sphinxcontrib.html>`_ suites of
-tools can be used to create specific types of diagrams:
-
-- `blockdiag examples <http://blockdiag.com/en/blockdiag/examples.html>`_
-- `nwdiag examples <http://blockdiag.com/en/nwdiag/nwdiag-examples.html>`_
-- `rackdiag examples <http://blockdiag.com/en/nwdiag/rackdiag-examples.html>`_
-- `seqdiag examples <http://blockdiag.com/en/seqdiag/examples.html>`_
-
-The styles applied to nodes and connections in these diagrams can be customized
-using `attributes
-<http://blockdiag.com/en/blockdiag/attributes/node.attributes.html>`_.
diff --git a/requirements.txt b/requirements.txt
index 2053e92..57a2bbc 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,18 +1,8 @@
-Sphinx~=2.4.4
-actdiag~=2.0.0
-blockdiag~=1.5.4
-doc8~=0.8.0
+Sphinx~=4.1.2
+doc8~=0.9.0
 docutils==0.16
-nwdiag~=2.0.0
 recommonmark~=0.6.0
-seqdiag~=2.0.0
-sphinx-rtd-theme~=0.4.3
-sphinxcontrib-actdiag~=2.0.0
-sphinxcontrib-blockdiag~=2.0.0
-sphinxcontrib-nwdiag~=2.0.0
+sphinx-rtd-theme~=0.5.2
 sphinxcontrib-openapi~=0.6.0
-sphinxcontrib-seqdiag~=2.0.0
-sphinxcontrib-spelling~=4.3.0
+sphinxcontrib-spelling~=7.2.1
 git+https://github.com/zdw/sphinx-multiversion@ec7c01cdaf2f9241245e84483dfb9bc0d0dffc62
-# sphinx-autoapi~=1.2.1
-# sphinxcontrib-golangdomain==0.2.0.dev0