metrics: remove dashing (unmaintained since 2016, archived)

- https://github.com/Shopify/dashing/commits/master

README.md

@@ -540,7 +540,6 @@ _See also: [awesome-selfhosted/Database Management](https://github.com/awesome-s
   - [Telegraf](https://github.com/influxdata/telegraf) - The plugin-driven server agent for collecting & reporting metrics.
 
 * Dashboards
-  - [Dashing](http://dashing.io/) - Ruby gem that allows for rapid statistical dashboard development. An all HTML5 approach allows for big screen displays in data centers or conference rooms.
   - [Facette](http://facette.io) - Time series data visualization and graphing software written in Go.
   - [Freeboard](https://github.com/Freeboard/freeboard) - A damn-sexy front-end real-time dashboard for the internet of things. Transforms raw JSON into delicious UI.
   - [Ganglia](http://ganglia.sourceforge.net/) - High performance, scalable RRD based monitoring for grids and/or clusters of servers. Compatible with Graphite using a single collection process.