Drop test for lower constraints

As we agreed, drop lower constraints test from stable branches to avoid
difficulty of maintaining package depencencies for the recent pip
dependency resolver.

Signed-off-by: Yasufumi Ogawa <yasufum.o@gmail.com>
Change-Id: Ifc3055086c2d0b14b5227105a0866a181f9446f0

.zuul.yaml

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

lower-constraints.txt

@@ -1,63 +0,0 @@
-appdirs==1.3.0
-Babel==2.3.4
-cliff==2.8.0
-cmd2==0.8.0
-coverage==4.0
-ddt==1.0.1
-debtcollector==1.2.0
-decorator==3.4.0
-deprecation==1.0
-dogpile.cache==0.6.2
-extras==1.0.0
-fixtures==3.0.0
-flake8==2.5.5
-hacking==0.12.0
-iso8601==0.1.11
-jmespath==0.9.0
-jsonpatch==1.16
-jsonpointer==1.13
-keystoneauth1==3.4.0
-linecache2==1.0.0
-mccabe==0.2.1
-mock==2.0.0
-monotonic==0.6
-msgpack-python==0.4.0
-munch==2.1.0
-netaddr==0.7.18
-netifaces==0.10.4
-openstacksdk==0.11.2
-os-client-config==1.28.0
-os-service-types==1.2.0
-osc-lib==1.8.0
-oslo.config==5.2.0
-oslo.context==2.19.2
-oslo.i18n==3.15.3
-oslo.log==3.36.0
-oslo.serialization==2.18.0
-oslo.utils==3.40.0
-pbr==2.0.0
-pep8==1.5.7
-positional==1.2.1
-prettytable==0.7.2
-pyflakes==0.8.1
-pyinotify==0.9.6
-pyparsing==2.1.0
-pyperclip==1.5.27
-python-dateutil==2.5.3
-python-keystoneclient==3.8.0
-python-mimeparse==1.6.0
-python-subunit==1.0.0
-pytz==2013.6
-PyYAML==3.12
-requests==2.14.2
-requests-mock==1.2.0
-requestsexceptions==1.2.0
-rfc3986==0.3.1
-simplejson==3.5.1
-six==1.10.0
-stestr==2.0.0
-stevedore==1.20.0
-testtools==2.2.0
-traceback2==1.4.0
-unittest2==1.1.0
-wrapt==1.7.0

tox.ini

@@ -53,9 +53,3 @@ exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,tools
 # F821 undefined name 'unicode'
 # if isinstance(config, str) or isinstance(config, unicode):
 builtins = unicode
-
-[testenv:lower-constraints]
-deps =
-  -c{toxinidir}/lower-constraints.txt
-  -r{toxinidir}/test-requirements.txt
-  -r{toxinidir}/requirements.txt