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: I95a19854bc55d92b63e1a826daf97e8b58711a07

lower-constraints.txt

@@ -1,51 +0,0 @@
-alembic==0.9.6
-cachetools==2.0.0
-coverage==4.0
-croniter==0.3.4
-doc8==0.8.1
-dogpile.cache==0.6.2
-eventlet==0.26.0
-fixtures==3.0.0
-Jinja2==2.10
-jsonschema==3.2.0
-keystonemiddleware==4.18.0
-kombu==4.6.1
-mistral-lib==2.3.0
-networkx==2.3
-nose==1.3.7
-oslo.concurrency==3.26.0
-oslo.config==6.8.0
-oslo.context==2.22.0
-oslo.db==4.40.0
-oslo.i18n==3.15.3
-oslo.log==3.36.0
-oslo.messaging==5.29.0
-oslo.middleware==3.31.0
-oslo.policy==3.6.0
-oslo.serialization==2.21.1
-oslo.service==2.1.0
-oslo.utils==4.0.0
-oslosphinx==4.7.0
-oslotest==3.2.0
-osprofiler==1.4.0
-paramiko==2.4.1
-pbr==2.0.0
-pecan==1.2.1
-Pygments==2.2.0
-PyJWT==1.5
-PyYAML==5.1
-requests-mock==1.2.0
-requests==2.18.0
-SQLAlchemy==1.2.5
-stestr==2.0.0
-stevedore==1.20.0
-tempest==21.0.0
-tenacity==5.0.1
-testtools==2.2.0
-tooz==1.58.0
-unittest2==1.1.0
-WebOb==1.7.1
-WebTest==2.0.27
-WSME==0.8.0
-yaql==1.1.3
-zake==0.1.6

tox.ini

@@ -129,9 +129,3 @@ extension =
     M330 = checks:check_python3_no_itervalues
     O323 = checks:check_oslo_namespace_imports
 paths = ./mistral/hacking
-
-[testenv:lower-constraints]
-deps =
-  -c{toxinidir}/lower-constraints.txt
-  -r{toxinidir}/test-requirements.txt
-  -r{toxinidir}/requirements.txt