remove announce and constraint jobs from pre-release pipeline

We do not want to send release announcement emails for
pre-releases (betas and alphas) because they are not complete.

We do not want to update the constraints list because pip requires
special instructions to use pre-releases and we do not use those
instructions in CI.

Change-Id: If1e608c7c2c7a8a775dcd61ca6fa3d64f3c16ae6
Signed-off-by: Doug Hellmann <doug@doughellmann.com>

zuul.d/project-templates.yaml

@@ -177,12 +177,6 @@
     pre-release:
       jobs:
         - release-openstack-python3
-        - announce-release:
-            dependencies:
-              - release-openstack-python3
-        - propose-update-constraints:
-            dependencies:
-              - release-openstack-python3
     release:
       jobs:
         - release-openstack-python3