defiant/rtl-tcp: get rid of bash

bash is depreciated.

hosts/defiant/services/rtl-tcp.nix

@@ -5,9 +5,9 @@ let
 in {
   hardware.rtl-sdr.enable = true;
   systemd.services.rtl-tcp = {
-    script = "${pkgs.rtl-sdr}/bin/rtl_tcp -a 0.0.0.0 -p ${toString port} -s 2000000 -T";
     serviceConfig = {
       Group = "plugdev";
+      ExecStart = "${pkgs.rtl-sdr}/bin/rtl_tcp -a 0.0.0.0 -p ${toString port} -s 2000000 -T";
     };
   };
   networking.firewall.allowedTCPPorts = [ port ];