remove api key requirement in plugin docs

[psilabs-dev]

The "api key requirement" probably shouldn't be specified in the query parameter, and it is not consistent with the other modules (e.g. shinobu, database), I'm suspecting this is just outdated documentation.

[Guerra24]

FYI

LANraragi/lib/LANraragi/Controller/Login.pm

Lines 65 to 66 in 1a12dbe

	# It can also be passed as a parameter. (Undocumented, mostly just meant for OPDS)
	my $param_key = $self->req->param('key') || '';

[psilabs-dev]

Right, I was imprecise. If it is specified, it's not mandatory, and either the other docs should include this as well, or we remove it from the docs, but currently it's not consistent (but also do we want credentials in query parameters, not headers?)

[Guerra24]

Went thru the changelogs because I couldn't remember why.

TL;DR: The API got reworked around 0.6.9~0.7.3. Key param got removed. Got restored in 0.8.8 for OPDS "only".

Should be fine to remove.

[Difegue]

Yeah it's technically possible to still use key as a queryparam everywhere, since even through it was restored for OPDS compliance I didn't make a separate auth sub just for it...

It's still better to be consistent in the documentation though so might as well remove the mentions.