we should drop the pulseaudio systemd user service file from systemd-services

It doesn't actually seem to work, because Alpine ships PA with autospawn = yes in client.conf, and anything that tries to use PA will cause PA to run (don't ask me how). This mechanism seems to also restart PA on crash. We could fork PA again to patch that out and create a user service file for it, but tbh it doesn't seem worth fighting with this if the current thing will restart it on crash, etc. Especially if we hope to phase out PA one day...

We should just drop the .service file from systemd-services because I think it's confusing to ship it when it's not used and not working correctly for us.

Note: I did not add this to the 'initial systemd' milestone because this isn't urgent/required. edit: it's actually required, see: !5142 (diffs)