Broken documentation link to prom.lib example file

[mmulich]

Custom formats can be defined. See prom.lib for examples.

This line of documentation in https://prometheus.io/docs/visualization/consoles/ results in a 404.

It seems to me that this console library mentioned is necessary for the example in the Consoles documentation.

[SuperQ]

Looks like it was removed in prometheus/prometheus#14807 as part of cleanup.