Dropping lower constraints testing

We facing errors related to the new pip resolver, this
topic was discussed on the ML and QA team proposed to
to test lower-constraints [1].

I propose to drop this test because the complexity and recurring pain needed
to maintain that now exceeds the benefits provided by this mechanismes.

[1] http://lists.openstack.org/pipermail/openstack-discuss/2020-December/019390.html

Change-Id: I53f3d2e4581d46abe150c80550b3875bb9ec73b4

lower-constraints.txt

@@ -1,140 +0,0 @@
-alembic==0.9.8
-amqp==2.2.2
-aodhclient==1.0.0
-appdirs==1.4.3
-beautifulsoup4==4.6.0
-cachetools==2.0.1
-certifi==2018.1.18
-chardet==3.0.4
-cliff==2.11.0
-cmd2==0.8.1
-contextlib2==0.5.5
-cotyledon==1.6.8
-coverage==4.5.1
-cryptography==2.7
-debtcollector==1.19.0
-deprecation==2.0
-dogpile.cache==0.6.5
-dulwich==0.19.0
-enum-compat==0.0.2
-eventlet==0.20.0
-extras==1.0.0
-fasteners==0.14.1
-fixtures==3.0.0
-future==0.16.0
-futurist==1.6.0
-gnocchiclient==3.3.1
-greenlet==0.4.13
-idna==2.6
-iso8601==0.1.12
-Jinja2==2.10
-jmespath==0.9.3
-jsonpatch==1.21
-jsonpointer==2.0
-keystoneauth1==3.6.2
-keystonemiddleware==4.21.0
-kombu==4.3.0
-linecache2==1.0.0
-logutils==0.3.5
-lxml==4.5.2
-Mako==1.0.7
-MarkupSafe==1.1.1
-monotonic==1.4
-mpmath==1.0.0
-msgpack==0.5.6
-munch==2.2.0
-netaddr==0.7.19
-netifaces==0.10.6
-networkx==2.4
-openstacksdk==0.12.0
-os-client-config==1.29.0
-os-service-types==1.2.0
-osc-lib==1.10.0
-oslo.cache==1.29.0
-oslo.concurrency==3.26.0
-oslo.config==6.8.0
-oslo.context==2.22.0
-oslo.db==4.44.0
-oslo.i18n==3.20.0
-oslo.log==3.44.0
-oslo.messaging==5.36.0
-oslo.middleware==3.35.0
-oslo.policy==3.6.0
-oslo.serialization==2.25.0
-oslo.service==1.30.0
-oslo.upgradecheck==1.3.0
-oslo.utils==3.40.0
-oslotest==3.3.0
-osprofiler==2.0.0
-packaging==17.1
-Paste==2.0.3
-PasteDeploy==1.5.2
-pbr==3.1.1
-pecan==1.2.1
-pika==0.10.0
-pika-pool==0.1.3
-ply==3.11
-prettytable==0.7.2
-pyasn1==0.4.2
-pycadf==2.7.0
-pyinotify==0.9.6
-PyJWT==1.6.0
-PyMySQL==0.8.0
-pyparsing==2.2.0
-pyperclip==1.6.0
-pysmi==0.2.2
-pysnmp==4.4.4
-python-ceilometerclient==2.9.0
-python-dateutil==2.7.0
-python-editor==1.0.3
-python-heatclient==1.14.0
-python-keystoneclient==3.15.0
-python-mimeparse==1.6.0
-python-mistralclient==3.3.0
-python-monascaclient==1.7.1
-python-neutronclient==6.7.0
-python-novaclient==10.1.0
-python-openstackclient==3.12.0
-python-subunit==1.2.0
-python-swiftclient==3.5.0
-python-troveclient==2.2.0
-pytz==2018.3
-PyYAML==5.1
-pyzabbix==0.7.4
-reno==3.1.0
-repoze.lru==0.7
-requests==2.20.0
-requests-mock==1.4.0
-requestsexceptions==1.4.0
-rfc3986==1.2.0
-Routes==2.4.1
-setproctitle==1.1.10
-simplejson==3.13.2
-SQLAlchemy==1.2.5
-sqlalchemy-migrate==0.11.0
-sqlparse==0.2.4
-statsd==3.2.2
-stestr==2.0.0
-stevedore==1.28.0
-sympy==1.1.1
-Tempita==0.5.2
-tenacity==4.12.0
-testresources==2.0.1
-testscenarios==0.5.0
-testtools==2.3.0
-traceback2==1.4.0
-unittest2==1.1.0
-urllib3==1.22
-vine==1.1.4
-voluptuous==0.11.1
-waitress==1.1.0
-WebOb==1.7.4
-WebTest==2.0.29
-Werkzeug==0.14.1
-wrapt==1.10.11
-docutils==0.11
-python-zaqarclient==1.2.0
-tooz==1.58.0
-zake==0.1.6
-psutil==5.4.3
-jsonschema==3.2.0

tox.ini

@@ -89,8 +89,3 @@ deps =
   -r{toxinidir}/doc/requirements.txt
 commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -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