hswaw/machines/customs: unpin hscloud/nixpkgs in certain modules

Change-Id: I1c02a485b76955e3de3859fca4d6c7e8e69ef09b
Reviewed-on: https://gerrit.hackerspace.pl/c/hscloud/+/1170
Reviewed-by: informatic <informatic@hackerspace.pl>
diff --git a/hswaw/machines/customs.hackerspace.pl/mikrotik-exporter.nix b/hswaw/machines/customs.hackerspace.pl/mikrotik-exporter.nix
index 8ea056e..ad18200 100644
--- a/hswaw/machines/customs.hackerspace.pl/mikrotik-exporter.nix
+++ b/hswaw/machines/customs.hackerspace.pl/mikrotik-exporter.nix
@@ -1,11 +1,6 @@
 { pkgs, ... }:
 
 let
-  unstable = import (fetchTarball {
-    sha256 = "0ww70kl08rpcsxb9xdx8m48vz41dpss4hh3vvsmswll35l158x0v";
-    url = "https://api.github.com/repos/NixOS/nixpkgs-channels/tarball/84d74ae9c9cbed73274b8e4e00be14688ffc93fe";
-  }) {config = pkgs.config; };
-
   name = "mikrotik-exporter";
   user = name;
   group = name;
@@ -28,6 +23,6 @@
     wantedBy    = [ "multi-user.target" ];
     serviceConfig.Type = "simple";
     serviceConfig.ExecStartPre = [ "!${prepare-secrets}" ];
-    serviceConfig.ExecStart = "${unstable.prometheus-mikrotik-exporter}/bin/mikrotik-exporter -config-file /mnt/secrets/${name}/ap.yml -port 127.0.0.1:9436";
+    serviceConfig.ExecStart = "${pkgs.prometheus-mikrotik-exporter}/bin/mikrotik-exporter -config-file /mnt/secrets/${name}/ap.yml -port 127.0.0.1:9436";
   };
 }