Update zuul queue configuration

Zuul is changing how queues are declared[1]. This patch drop
the explicit queue definition for Designate client since it is inherited
via the designate-devstack-jobs template.

This change also drops the `lower-constraints` job and amends the doc
requirements to match global requirements.

[1] https://lists.zuul-ci.org/pipermail/zuul-discuss/2022-May/001801.html

Change-Id: Ibf3bab374ec3a5bec842051c29d18864d42c02b8
(cherry picked from commit ef2098e654)

.zuul.yaml

@@ -3,11 +3,8 @@
       - check-requirements
       - designate-devstack-jobs
       - openstack-cover-jobs
-      - openstack-lower-constraints-jobs
       - openstack-python-jobs
       - openstack-python35-jobs
       - openstack-python36-jobs
       - openstackclient-plugin-jobs
       - publish-openstack-docs-pti
-    gate:
-      queue: designate

doc/requirements.txt

@@ -1,5 +1,6 @@
 # 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.
-sphinx!=1.6.6,!=1.6.7,>=1.6.2 # BSD
+sphinx!=1.6.6,!=1.6.7,>=1.6.2,<2.0.0;python_version=='2.7'  # BSD
+sphinx!=1.6.6,!=1.6.7,>=1.6.2;python_version>='3.4'  # BSD
 openstackdocstheme>=1.18.1 # Apache-2.0