puppet: Remove python-dateutil requirement from pg_backup_and_purge.
puppet: Remove python-dateutil requirement from pg_backup_and_purge.

1f565a9f41 removed the `package` lines which install
`python-dateutil`, but not the line in `puppet_ops` that reference it;
as such, Puppet manifests in puppet_ops fail to compile.

Remove the stale reference to `python-dateutil`, which is unnecessary
since the code is python3, not python2.

punchagan/zulip,eeshangarg/zulip,eeshangarg/zulip,zulip/zulip,andersk/zulip,kou/zulip,hackerkid/zulip,hackerkid/zulip,hackerkid/zulip,rht/zulip,kou/zulip,brainwane/zulip,zulip/zulip,zulip/zulip,synicalsyntax/zulip,brainwane/zulip,synicalsyntax/zulip,andersk/zulip,timabbott/zulip,shubhamdhama/zulip,showell/zulip,synicalsyntax/zulip,eeshangarg/zulip,eeshangarg/zulip,zulip/zulip,andersk/zulip,kou/zulip,showell/zulip,hackerkid/zulip,kou/zulip,zulip/zulip,showell/zulip,zulip/zulip,kou/zulip,zulip/zulip,shubhamdhama/zulip,punchagan/zulip,synicalsyntax/zulip,brainwane/zulip,synicalsyntax/zulip,punchagan/zulip,showell/zulip,hackerkid/zulip,synicalsyntax/zulip,punchagan/zulip,shubhamdhama/zulip,shubhamdhama/zulip,timabbott/zulip,brainwane/zulip,synicalsyntax/zulip,rht/zulip,shubhamdhama/zulip,hackerkid/zulip,hackerkid/zulip,timabbott/zulip,punchagan/zulip,brainwane/zulip,rht/zulip,timabbott/zulip,rht/zulip,shubhamdhama/zulip,showell/zulip,andersk/zulip,rht/zulip,andersk/zulip,eeshangarg/zulip,andersk/zulip,rht/zulip,timabbott/zulip,shubhamdhama/zulip,timabbott/zulip,kou/zulip,andersk/zulip,punchagan/zulip,punchagan/zulip,eeshangarg/zulip,timabbott/zulip,brainwane/zulip,rht/zulip,brainwane/zulip,showell/zulip,eeshangarg/zulip,showell/zulip,kou/zulip