Remove obsolete pings and/or metrics

[alexgibson]

We have several custom pings that we no longer use (interaction, non-interaction, page_view) but they are still featured in the Glean dictionary for bedrock:

https://dictionary.telemetry.mozilla.org/apps/bedrock?itemType=pings&page=1

It would be nice if the dictionary auto updated when things are removed from a website's metrics/pings schema. This will make it less confusing since people would not be left wondering what's in use and what's not.