Dropping lower constraints references

As a follow up to Ied61e65006ad54803453776e763594e216be1353,
remove the lower-constraints.txt file and its references.

Change-Id: I2baa6d318cdbbf86da86cc94171cc7714dbdba3a

lower-constraints.txt

@@ -1,69 +0,0 @@
-amqp==2.1.1
-appdirs==1.3.0
-Babel==2.3.4
-bandit==1.4.0
-cachetools==2.0.0
-contextlib2==0.4.0
-coverage==4.0
-debtcollector==1.2.0
-eventlet==0.18.2
-extras==1.0.0
-fasteners==0.7.0
-fixtures==3.0.0
-futurist==1.2.0
-gitdb==0.6.4
-GitPython==1.0.1
-greenlet==0.4.15
-iso8601==0.1.11
-Jinja2==2.10
-jsonschema==3.2.0
-keystoneauth1==3.4.0
-kombu==4.0.0
-linecache2==1.0.0
-MarkupSafe==1.1.1
-mox3==0.20.0
-msgpack-python==0.4.0
-netaddr==0.7.18
-netifaces==0.10.4
-os-client-config==1.28.0
-oslo.concurrency==3.26.0
-oslo.config==5.2.0
-oslo.context==2.19.2
-oslo.i18n==3.15.3
-oslo.log==3.36.0
-oslo.messaging==5.29.0
-oslo.middleware==3.31.0
-oslo.serialization==2.18.0
-oslo.service==1.24.0
-oslo.utils==4.7.0
-oslotest==3.2.0
-Paste==2.0.2
-PasteDeploy==1.5.0
-pbr==2.0.0
-pika==0.10.0
-pika-pool==0.1.3
-prettytable==0.7.2
-pyinotify==0.9.6
-pyparsing==2.1.0
-python-dateutil==2.5.3
-python-mimeparse==1.6.0
-python-subunit==1.0.0
-pytz==2013.6
-PyYAML==3.13
-repoze.lru==0.7
-requests==2.14.2
-requestsexceptions==1.2.0
-rfc3986==0.3.1
-Routes==2.3.1
-six==1.10.0
-smmap==0.9.0
-statsd==3.2.1
-stestr==2.0.0
-stevedore==1.20.0
-tenacity==3.2.1
-testtools==2.2.0
-traceback2==1.4.0
-unittest2==1.1.0
-vine==1.1.4
-WebOb==1.7.1
-wrapt==1.7.0

tox.ini

@@ -38,12 +38,6 @@ commands =
   rm -rf releasenotes/build
   sphinx-build -a -E -W -d releasenotes/build/doctrees --keep-going -b html releasenotes/source releasenotes/build/html
 
-[testenv:lower-constraints]
-deps =
-  -c{toxinidir}/lower-constraints.txt
-  -r{toxinidir}/test-requirements.txt
-  -r{toxinidir}/requirements.txt
-
 [flake8]
 # E123, E125 skipped as they are invalid PEP-8.
 # W504 skipped as you must choose this or W503