bitcoind: simplify pruning

Remove the possible null value for bitcoind.prune and set prune = 0 in
bitcoind as a default. Remove prune = 0 in secure-node.nix and the
mkForce in configuration.nix (bitcoind.prune = lib.mkForce ).

examples/configuration.nix

@@ -27,8 +27,7 @@
   # clightning is compatible with pruning. See
   # https://github.com/ElementsProject/lightning/#pruning for more information.
   # LND and electrs are not compatible with pruning.
-  # Note: You can override default settings from secure-node.nix as follows
-  # services.bitcoind.prune = lib.mkForce 100000;
+  # services.bitcoind.prune = 100000;
   #
   # You can add options that are not defined in modules/bitcoind.nix as follows
   # services.bitcoind.extraConfig = ''

modules/bitcoind.nix

@@ -12,7 +12,7 @@ let
 
     ${optionalString cfg.testnet "testnet=1"}
     ${optionalString (cfg.dbCache != null) "dbcache=${toString cfg.dbCache}"}
-    ${optionalString (cfg.prune != null) "prune=${toString cfg.prune}"}
+    "prune=${toString cfg.prune}
     ${optionalString (cfg.sysperms != null) "sysperms=${if cfg.sysperms then "1" else "0"}"}
     ${optionalString (cfg.disablewallet != null) "disablewallet=${if cfg.disablewallet then "1" else "0"}"}
     ${optionalString (cfg.assumevalid != null) "assumevalid=${cfg.assumevalid}"}
@@ -179,12 +179,8 @@ in {
         description = "Override the default database cache size in megabytes.";
       };
       prune = mkOption {
-        type = types.nullOr (types.coercedTo
-          (types.enum [ "disable" "manual" ])
-          (x: if x == "disable" then 0 else 1)
-          types.ints.unsigned
-        );
-        default = null;
+        type = types.ints.unsigned;
+        default = 0;
         example = 10000;
         description = ''
           Reduce storage requirements by enabling pruning (deleting) of old

modules/presets/secure-node.nix

@@ -64,7 +64,6 @@ in {
       addnodes = [ "ecoc5q34tmbq54wl.onion" ];
       discover = false;
       addresstype = "bech32";
-      prune = 0;
       dbCache = 1000;
     };
     services.tor.hiddenServices.bitcoind = mkHiddenService { port = cfg.bitcoind.port; };