disable hardened kernel profile

- The hardened profile significantly decreases performance
  (and potentially stability)
- In the spirit of the nix-bitcoin security fund, nixbitcoin.org serves
  as a public target. It should therefore have the same security
  characteristics as a basic nix-bitcoin system that doesn't use the
  hardened profile.

configuration.nix

@@ -2,7 +2,6 @@
 {
   imports = [
     <nix-bitcoin/modules/presets/secure-node.nix>
-    <nix-bitcoin/modules/presets/hardened.nix>
 
     ./base.nix
     ./website