Drop lower-constraints.txt and its testing

As discussed in TC PTG[1] and TC resolution[2], we are
dropping the lower-constraints.txt file and its testing.
We will keep lower bounds in the requirements.txt file but
with a note that these are not tested lower bounds and we
try our best to keep them updated.

[1] https://etherpad.opendev.org/p/tc-zed-ptg#L326
[2] https://governance.openstack.org/tc/resolutions/20220414-drop-lower-constraints.html#proposal

Change-Id: I0fc96a3e9ce4626a9f137c1af02c738330235c43

.zuul.yaml

@@ -1,7 +1,6 @@
 - project:
     templates:
       - check-requirements
-      - openstack-lower-constraints-jobs
     check:
       jobs:
         - openstack-tox-pep8

lower-constraints.txt

@@ -1,16 +0,0 @@
-Babel==2.5.3
-bashate==2.1.0
-decorator==4.2.1
-dib-utils==0.0.8
-diskimage-builder==1.1.2
-flake8==3.6.0
-hacking==3.0.1
-mccabe==0.6.0
-networkx==1.11
-pbr==2.0.0
-pep8==1.5.7
-pyflakes==2.0.0
-pytz==2018.3
-PyYAML==3.12
-six==1.11.0
-stevedore==1.28.0

requirements.txt

@@ -1,3 +1,7 @@
+# Requirements lower bounds listed here are our best effort to keep them up to
+# date but we do not test them so no guarantee of having them all correct. If
+# you find any incorrect lower bounds, let us know or propose a fix. 
+
 # The order of packages is significant, because pip processes them in the order
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.

tox.ini

@@ -37,9 +37,3 @@ ignore=safe_sudo
 show-source = true
 builtins = _
 exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,tools
-
-[testenv:lower-constraints]
-deps =
-  -c{toxinidir}/lower-constraints.txt
-  -r{toxinidir}/test-requirements.txt
-  -r{toxinidir}/requirements.txt