[stable] Drop lower-constraints job

As discussed in neutron team meeting [1], it is not worth fixing issues
identified by new pip resolver in stable branches. So let's drop the job

For ussuri, add isort to test-requirements from original fix attempt [2]

[1] http://eavesdrop.openstack.org/meetings/networking/2021/networking.2021-01-12-14.00.log.html#l-164
[2] https://review.opendev.org/c/openstack/networking-sfc/+/748135
Conflicts:
	lower-constraints.txt
	zuul.d/project.yaml

Change-Id: Ic62b63fd2e1f314f6c465a259df75d197180e1f9
(cherry picked from commit 1a51c0f)

test-requirements.txt

@@ -16,5 +16,6 @@ oslotest>=3.2.0 # Apache-2.0
 stestr>=2.0.0 # Apache-2.0
 astroid==1.6.5 # LGPLv2.1
 pylint==1.9.2 # GPLv2
+isort==4.3.21 # MIT
 psycopg2>=2.7.7 # LGPL/ZPL
 PyMySQL>=0.7.6 # MIT License

tox.ini

@@ -118,12 +118,6 @@ commands = oslo-config-generator --config-file etc/oslo-config-generator/network
 [testenv:genpolicy]
 commands = oslopolicy-sample-generator --config-file=etc/oslo-policy-generator/policy.conf
 
-[testenv:lower-constraints]
-deps =
-  -c{toxinidir}/lower-constraints.txt
-  -r{toxinidir}/test-requirements.txt
-  -r{toxinidir}/requirements.txt
-
 [testenv:dev]
 # run locally (not in the gate) using editable mode
 # https://pip.pypa.io/en/stable/reference/pip_install/#editable-installs

zuul.d/project.yaml

@@ -1,6 +1,5 @@
 - project:
     templates:
-      - openstack-lower-constraints-jobs-neutron
       - openstack-python3-ussuri-jobs-neutron
       - publish-openstack-docs-pti
       - check-requirements