Remove "mitogen" library installation from "docs" job

Since pyroute 0.6.2, this dependency is not needed anymore. The
pyroute version is bumped both in requirements and doc/requirements.

This patch bumps the pyroute2 version to 0.6.4 (newest version
provided in upper-requirements).

Change-Id: I627e902e32fe59c6829c3bc92af19abff4b70f9a
Related-Bug: #1928913

doc/requirements.txt

@@ -8,4 +8,4 @@ oslotest>=3.2.0 # Apache-2.0
 reno>=3.1.0 # Apache-2.0
 # NOTE(ralonsoh): pyroute2 module should be installed and the version limited
 # according to upper-constraints.txt
-pyroute2>=0.5.13;sys_platform!='win32' # Apache-2.0 (+ dual licensed GPL2)
+pyroute2>=0.6.4;sys_platform!='win32' # Apache-2.0 (+ dual licensed GPL2)

lower-constraints.txt

@@ -97,7 +97,7 @@ PyMySQL==0.7.6
 pyOpenSSL==17.1.0
 pyparsing==2.1.0
 pyperclip==1.5.27
-pyroute2==0.5.13
+pyroute2==0.6.4
 python-dateutil==2.7.0
 python-designateclient==2.7.0
 python-editor==1.0.3

requirements.txt

@@ -48,7 +48,7 @@ ovs>=2.10.0 # Apache-2.0
 ovsdbapp>=1.10.0 # Apache-2.0
 packaging>=20.4  # Apache-2.0
 psutil>=5.3.0 # BSD
-pyroute2>=0.5.13;sys_platform!='win32' # Apache-2.0 (+ dual licensed GPL2)
+pyroute2>=0.6.4;sys_platform!='win32' # Apache-2.0 (+ dual licensed GPL2)
 pyOpenSSL>=17.1.0 # Apache-2.0
 
 python-novaclient>=9.1.0 # Apache-2.0

tox.ini

@@ -141,9 +141,6 @@ envdir = {toxworkdir}/docs
 deps =
   -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/doc/requirements.txt
-# NOTE(slaweq): mitogen is optional dependency of the pyroute2 and without it
-# our docs job is failing
-  mitogen>=0.2.9
 commands = sphinx-build -W -b html doc/source doc/build/html
 
 [testenv:pdf-docs]