Use propose-updates for requirements-constraints

We don't need a legacy job for this, we have a propose-updates job that
can do any of the tagets the script knows about.

We do need to add git-review to the remote host though, so do that.

Change-Id: I3cf10120ab0e9aff65c35468d3a7bb9d42725712

playbooks/proposal/pre.yaml

@@ -1,4 +1,8 @@
 - hosts: all
+  pre-tasks:
+    - name: Install git-review
+      command: pip install git-review
+      become: yes
   roles:
     - legacy-copy-project-config-scripts
     - add-sshkey

zuul.d/projects.yaml

@@ -29236,7 +29236,9 @@
         - release-wheel-mirror:
             dependencies:
               - build-wheel-mirror
-        - legacy-propose-requirements-constraints-master
+        - propose-updates:
+            vars:
+              update_target: requirements-constraints
     templates:
       - system-required
       - openstack-pypy-jobs-nonvoting