Replace ad-hoc output splitting hacks with multiple outputs

[abbradar]

Issue description

Now that multiple outputs branch has landed we can replace ad-hoc splitting hacks with it. avn from IRC suggested to do this for PulseAudio. This might be a simple task -- leaving it here to not lose it in the noise.

[avnik]

ffado, jackaudio, kerberos (both heimdal and krb5), nghttp2 as well.

[vcunat]

IIRC go packages often override outputs attribute in the resulting attrmap. Such use cases should be solved by setting meta.outputsToInstall instead, at least after merging NixOS/nix#815. (EDITs: sentence clarity)

[Ekleog]

(triage) Does it make sense to keep this issue open?

[avnik]

Still actual ;(

May be would be good to create separate issues for each affected package?
(git grep libOnly shows them all). Although I try to fix at least some of them.

[edolstra]

Yes, separate issues would be more useful.

[avnik]

Well, I definelly know how (and would like) to do it for pulseaudio, although jack2 and ffado mutually depends on each other, and libOnly breaks this loop at least partially

[avnik]

I revive it as PR, because at least biggest part of sound-related stuff is a solvable.