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

This also makes the following two changes to fix the broken CI.

- Switch the python3 job template to unversioned one because
  the heat-cfntools project follows an independent release model.
  This effectively removes py36 tests.

- Use upper-constraints.txt to build documentation, to avoid pulling
  the latest Sphinx which includes a breaking change.

Change-Id: I3c41ed7cd54e8c8d3fad05ea7ac86fc35b9fa4d1

1 files changed, 1 insertions, 1 deletions

diff --git a/doc/source/conf.py b/doc/source/conf.py
index 764df86..1745f8e 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -65,7 +65,7 @@ copyright = 'OpenStack Foundation'
 #
 # This is also used if you do content translation via gettext catalogs.
 # Usually you set "language" from the command line for these cases.
-language = None
+language = 'en'
 
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.