imp: usePeersFromLedgerAfterSlot -> useLedgerAfterSlot

* Update usePeersFromLedgerAfterSlot to useLedgerAfterSlot for
  consistent naming with the cardano-node topology file key.

* It would be nice to put a deprecated warn for the legacy name in the
  environment for some time before removing it, but with eager
  evaluation of the cardanoLib environment set, either everybody sees
  the warn if present, or nobody does if missing.  Since grep.app
  doesn't find any downstream uses of the legacy name beyond the repos
  already being updated, we'll simply remove the legacy named attr now.

cardano-lib/default.nix

@@ -66,7 +66,7 @@ let
       inherit (env) edgeNodes;
 
       bootstrapPeers = map (e: {address = e.addr; inherit (e) port;}) env.edgeNodes;
-      useLedgerAfterSlot = env.usePeersFromLedgerAfterSlot;
+      useLedgerAfterSlot = env.useLedgerAfterSlot;
     };
   in
     if (env.nodeConfig.EnableP2P or false)
@@ -166,7 +166,7 @@ let
       confKey = "mainnet_full";
       networkConfig = import ./mainnet-config.nix // minNodeVersion;
       networkConfigBp = import ./mainnet-config-bp.nix // minNodeVersion;
-      usePeersFromLedgerAfterSlot = 148350000;
+      useLedgerAfterSlot = 148350000;
       extraDbSyncConfig = {
         enableFutureGenesis = true;
       };
@@ -195,7 +195,7 @@ let
       edgePort = 3001;
       networkConfig = import ./preprod-config.nix // minNodeVersion;
       networkConfigBp = import ./preprod-config-bp.nix // minNodeVersion;
-      usePeersFromLedgerAfterSlot = 83894000;
+      useLedgerAfterSlot = 83894000;
       extraDbSyncConfig = {
         enableFutureGenesis = true;
       };
@@ -224,7 +224,7 @@ let
       edgePort = 3001;
       networkConfig = import ./preview-config.nix // minNodeVersion;
       networkConfigBp = import ./preview-config-bp.nix // minNodeVersion;
-      usePeersFromLedgerAfterSlot = 73267000;
+      useLedgerAfterSlot = 73267000;
       extraDbSyncConfig = {
         enableFutureGenesis = true;
       };