website-update: Don't define SITEDIR in the script.

Prefer setting WorkingDirectory.

website-update: Remove lockdir code.

Now that we're running as a systemd service, that will make sure
only one update runs at a time.

website-update: Stop updating the database.

Move this to a separate service.

website-update: Make sqlite loading more robust.

* Bail on the first error.
* Allow 30 seconds to open a locked table.

cron: Exclude what are obviously scripts from compilation.

The impetus here is to stop the script from trying to compile and
complaining about
<www/conservancy/static/projects/policies/publish-travel-policy.py>, which
is a script written in Python 3 meant to help with repository maintenance.

Excluding files with `-` in the name seems reasonable since they can't be
modules anyway, so there's no reason to compile them.

This will start failing if we add a similar script later that doesn't have a
`-` in its name.