security: update /proc restriction mechanism

NixOS option `security.hideProcessInformation` for globally restricting
access to /proc has been removed.
Use per-service restrictions via 'ProtectProc' instead.

Rename
`nix-bitcoin.security.hideProcessInformation` to
`nix-bitcoin.security.dbusHideProcessInformation`
because this option now only implements the dbus restriction.

pkgs/lib.nix

@@ -17,9 +17,8 @@ let self = {
       ProtectKernelModules = "true";
       ProtectKernelLogs = "true";
       ProtectClock = "true";
-      # Test and enable these when systemd v247 is available
-      # ProtectProc = "invisible";
-      # ProcSubset = "pid";
+      ProtectProc = "invisible";
+      ProcSubset = "pid";
       ProtectControlGroups = "true";
       RestrictAddressFamilies = "AF_UNIX AF_INET AF_INET6";
       RestrictNamespaces = "true";