This reverts commit 3387035400.

Enabling `jinja2_native` does help with the issue it is trying to
address - #151 (Github Pull Request), but it introduces a regression
when generating templates.

An example is
`roles/matrix-nginx-proxy/templates/nginx/conf.d/matrix-riot-web.conf.j2`,
which yields a strange resulting value of:

```
location /.well-known/acme-challenge {
    resolver 127.0.0.11 valid=5s;
    set $backend "matrix-certbot:8080";
    proxy_pass http://$backend;

    resolver 127.0.0.11 valid=5s;
    set $backend "matrix-certbot:8080";
    proxy_pass http://$backend;
}
```

For whatever reason (still to be investigated), the `if` block's
contents seem to have been outputted twice.

Reverting until this is resolved.
Until then, #151 would rely on the workaround and not on `jinja2_native`.

Helps with #151 (Github Pull Request), but only for Ansible >= 2.7
and when Jinja >= 2.10 is in use.

For other version combinations we still need the workaround proposed
in the pull rqeuest.