pulseaudio nixos module: use the units provided by upstream (#21633)

I have left in 2 NixOS custom config directives, so the configuration
should be the same with the only change in behaviour being that the
service is not eagerly loaded but in fact only socket activated, which
it should be.

nixos/modules/config/pulseaudio.nix

@@ -212,6 +212,7 @@ in {
       # Allow PulseAudio to get realtime priority using rtkit.
       security.rtkit.enable = true;
 
+      systemd.packages = [ cfg.package ];
     })
 
     (mkIf hasZeroconf {
@@ -227,31 +228,14 @@ in {
         target = "pulse/default.pa";
         source = myConfigFile;
       };
-
       systemd.user = {
         services.pulseaudio = {
-          description = "PulseAudio Server";
-          # NixOS doesn't support "Also" so we bring it in manually
-          wantedBy = [ "default.target" ];
           serviceConfig = {
-            Type = "notify";
-            ExecStart = binaryNoDaemon;
-            Restart = "on-failure";
             RestartSec = "500ms";
           };
           environment = { DISPLAY = ":${toString config.services.xserver.display}"; };
           restartIfChanged = true;
         };
-
-        sockets.pulseaudio = {
-          description = "PulseAudio Socket";
-          wantedBy = [ "sockets.target" ];
-          socketConfig = {
-            Priority = 6;
-            Backlog = 5;
-            ListenStream = "%t/pulse/native";
-          };
-        };
       };
     })