Some pictures use old fluentd logo

These files are using old fluentd/fluent-bit logo.

```
public/favicon.ico
public/images/fluentd-website-banner.png
public/images/fluentd_unified_logging_architecture.png
public/images/fluentd_usecase_adtech_application_logging.png
public/images/fluentd_usecase_applogging.png
public/images/fluentd_usecase_gaming_application_logging.png
public/images/syslog-fluentd-alert.png
public/images/blog/unified-logging-pluggable.png
tmpl-assets/img/architecture/log-as-json.png
tmpl-assets/img/miscellany/fluent-bit-banner.png
tmpl-assets/img/recipes/after-fluentd-rsyslogd.png
tmpl-assets/img/recipes/docker-fluentd.png
tmpl-assets/img/recipes/elasticsearch-s3-fluentd.png
tmpl-assets/img/recipes/fluentd_docker.png
tmpl-assets/img/recipes/fluentd_docker_integrated.png
tmpl-assets/img/recipes/syslog-fluentd-influxdb.png
```

And new style architecture is not contained in this repository.
It is used `http://docs.fluentd.org/images/fluentd-architecture.png`