nixos manuals: bring back package references

This reverts most of 89e983786a, as those references are sanitized now.
Fixes #10039, at least most of it.

The `sane` case wasn't fixed, as it calls a *function* in pkgs to get
the default value.

nixos/modules/services/misc/subsonic.nix

@@ -97,6 +97,7 @@ in
 
       transcoders = mkOption {
         type = types.listOf types.path;
+        default = [ "${pkgs.ffmpeg}/bin/ffmpeg" ];
         description = ''
           List of paths to transcoder executables that should be accessible
           from Subsonic. Symlinks will be created to each executable inside
@@ -152,8 +153,5 @@ in
     };
 
     users.extraGroups.subsonic.gid = config.ids.gids.subsonic;
-
-    services.subsonic.transcoders = mkDefault [ "${pkgs.ffmpeg}/bin/ffmpeg" ];
-
   };
 }