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: Iccaf7cfb8051ec1b01fde0786489855013297703

.zuul.yaml

@@ -1,7 +1,6 @@
 - project:
     templates:
       - check-requirements
-      - openstack-lower-constraints-jobs
       - openstack-python3-wallaby-jobs
       - publish-openstack-docs-pti
       - release-notes-jobs-python3

lower-constraints.txt

@@ -1,51 +0,0 @@
-alabaster==0.7.10
-appdirs==1.3.0
-Babel==2.3.4
-coverage==4.0
-debtcollector==1.2.0
-docutils==0.11
-doc8==0.6.0
-dulwich==0.15.0
-eventlet==0.20.0
-extras==1.0.0
-fixtures==3.0.0
-flake8==2.5.5
-hacking==0.12.0
-imagesize==0.7.1
-iso8601==0.1.11
-Jinja2==2.10
-keystoneauth1==3.4.0
-linecache2==1.0.0
-MarkupSafe==1.0
-mccabe==0.2.1
-monotonic==0.6
-mox3==0.20.0
-msgpack-python==0.4.0
-netaddr==0.7.18
-netifaces==0.10.4
-os-client-config==1.28.0
-oslo.i18n==3.15.3
-oslo.log==3.36.0
-oslo.serialization==2.21.1
-oslo.utils==3.33.0
-oslotest==3.2.0
-pbr==2.0.0
-pep8==1.5.7
-pyflakes==0.8.1
-Pygments==2.2.0
-pyparsing==2.1.0
-python-mimeparse==1.6.0
-python-subunit==1.0.0
-pytz==2013.6
-PyYAML==3.12
-requests==2.18.0
-requestsexceptions==1.2.0
-snowballstemmer==1.2.1
-stestr==2.0.0
-stevedore==1.20.0
-testrepository==0.0.18
-testtools==2.2.0
-traceback2==1.4.0
-unittest2==1.1.0
-wrapt==1.7.0
-yaql==1.1.3 # Apache 2.0 License

tox.ini

@@ -66,9 +66,3 @@ show-source = True
 ignore = E123,E125,W504
 builtins = _
 exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,build
-
-[testenv:lower-constraints]
-deps =
-  -c{toxinidir}/lower-constraints.txt
-  -r{toxinidir}/test-requirements.txt
-  -r{toxinidir}/requirements.txt