netns: remove conditionals for service settings

Going without the conditionals (like in secure-node.nix) adds
readability and doesn't reduce evaluation performance (in fact, it
even slightly improves performance due to implementation details
of mkIf).

To avoid errors, remove use of disabled services in secure-node.nix and
nix-bitcoin-webindex.nix.

modules/presets/secure-node.nix

@@ -194,7 +194,9 @@ in {
       port = 50001;
       enforceTor = true;
     };
-    services.tor.hiddenServices.electrs = mkHiddenService { port = cfg.electrs.port; toHost = cfg.electrs.address; };
+    services.tor.hiddenServices.electrs = mkIf cfg.electrs.enable (mkHiddenService {
+      port = cfg.electrs.port; toHost = cfg.electrs.address;
+    });
 
     services.spark-wallet = {
       onion-service = true;