bug#49004: Update IRC-related references to point to Libera.Chat

[J.P.]

The changes to `erc-networks-alist' may warrant further discussion at
some point (see below if you're really interested). Otherwise, I'd say
everything looks fine. Let me know if you need someone to actually fire
it up. I think you've already field tested the changes to erc-services
though, right? Thanks.


Below
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`erc-networks-alist' isn't consulted for libera at the moment because
the RPL_ISUPPORT NETWORK token takes precedence.

Trusted opinions vary on whether clients should be using this param for
anything other than display purposes. But there's currently no viable
alternative offered by naysayers for canonical/authoritative,
server-reported network identifiers.

We don't currently have a policy in place for handing some hypothetical
encounter with an undesirable NETWORK name, such as NETWORK=My\x20Net,
that we'd rather not use as an identifying lisp symbol (unless we're
cool with passing around 'My\ Net).

Again, this doesn't matter at this exact second, but I'm hoping to
cross that bridge relatively shortly.