nix: remove outdated note requiring managed daemon for distributedBuilds

For Nix 1, some environment variables were set when using distributed
builds requiring the Nix daemon to be managed by nix-darwin. However,
support for Nix 1 has been removed and no other environment variables
for Nix are set by default.

modules/nix/default.nix

@@ -191,9 +191,6 @@ in
         description = ''
           Whether to distribute builds to the machines listed in
           {option}`nix.buildMachines`.
-
-          NOTE: This requires services.nix-daemon.enable for a
-          multi-user install.
         '';
       };