Remove obsolete NodeObject fields:

Legacy fields of NodeObject are removed, as they are no longer
used and there is a space savings from omitting them:

* Remove LedgerIndex

src/ripple/app/ledger/Ledger.cpp

@@ -688,7 +688,7 @@ bool Ledger::saveValidatedLedger (bool current)
         s.add32 (HashPrefix::ledgerMaster);
         addRaw (s);
         getApp().getNodeStore ().store (
-            hotLEDGER, mLedgerSeq, std::move (s.modData ()), mHash);
+            hotLEDGER, std::move (s.modData ()), mHash);
     }
 
     AcceptedLedger::pointer aLedger;