Dropping lower constraints testing (stable Xena)

This topic was discussed on the ML and QA team proposed to
to test lower-constraints [1].

As decided in Neutron meeting, stable branches will drop this
CI job [2].

[1]http://lists.openstack.org/pipermail/openstack-discuss/2020-December/019390.html
[2]http://eavesdrop.openstack.org/meetings/networking/2021/networking.2021-01-12-14.00.log.html

To pass gates, this squashes the PEP8 fix from Change-Id
I8e58da2d88d727018c8d5af5949e34f8c0893c1f:

Skip B105 pep8 error: hardcoded passwords

Skip B105 pep8 error:
* https://bandit.readthedocs.io/en/latest/plugins/b105_hardcoded_password_string.html
* https://cwe.mitre.org/data/definitions/259.html

Trivial-Fix

(cherry picked from commit 28628e8f96)

Change-Id: Id2da075b367281bb5081333e37e472f1e8921e44

.zuul.yaml

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

tox.ini

@@ -81,8 +81,11 @@ enable-extensions=H904
 
 [testenv:bandit]
 # B303: blacklist calls: md5, sha1
+# B105: The software contains a hard-coded password, which it uses for its own
+#       inbound authentication or for outbound communication to external
+#       components.
 deps = -r{toxinidir}/test-requirements.txt
-commands = bandit -r neutronclient -x tests -n5 -s B303
+commands = bandit -r neutronclient -x tests -n5 -s B303,B105
 
 [testenv:lower-constraints]
 deps =