Remove lower-constraints job

As discussed during the upstream ironic community meeting on
Monday Dec 14 2020, the lower-constraints job is being removed.

Also Cap version of ipa-builder to 2.2.0

Versions higher than 2.2.0 of ironic-python-agent-builder use
tinycore 11.x to build tinyipa, and that uses a kernel too recent
to be built on bionic.

Change-Id: Iab279c57676dba8faa87ab7523e577d3b65eb428
(cherry picked from commit 0bbba8e62f)
(cherry picked from commit d5ae74e9b8)

zuul.d/ironic-lib-jobs.yaml

@@ -13,6 +13,8 @@
       - ^tox.ini$
     required-projects:
       - openstack/ironic-lib
+      - name: openstack/ironic-python-agent-builder
+        override-checkout: 2.2.0
     vars:
       devstack_localrc:
         IRONIC_RAMDISK_TYPE: tinyipa

zuul.d/project.yaml

@@ -2,7 +2,6 @@
     templates:
       - check-requirements
       - openstack-cover-jobs
-      - openstack-lower-constraints-jobs
       - openstack-python3-ussuri-jobs
       - publish-openstack-docs-pti
     check: