Rockbox IRC channels migrated to Libera.chat

[speachy]

As of 2021-05-23, the #rockbox and #rockbox-community IRC channels have been migrated over to Libera.chat.

Why make this move?  By now the drama about Freenode's change in management is fairly well known, and to be frank, the new operators
have not demonstrated much in the way of trustworthiness.

The old channels on Freenode will remain as unmonitered/unlogged placeholders as long as the new Freenode operators permit.