refactor: inline constant return value of CDBWrapper::WriteBatch

`WriteBatch` can only ever return `true` - its errors are handled by throwing a `throw dbwrapper_error` instead.
The boolean return value is quite confusing, especially since it's symmetric with `CDBWrapper::Read`, which catches the exceptions and returns a boolean instead.
We're removing the constant return value and inlining `true` for its usages.

src/node/blockstorage.cpp

@@ -88,7 +88,8 @@ bool BlockTreeDB::WriteBatchSync(const std::vector<std::pair<int, const CBlockFi
     for (const CBlockIndex* bi : blockinfo) {
         batch.Write(std::make_pair(DB_BLOCK_INDEX, bi->GetBlockHash()), CDiskBlockIndex{bi});
     }
-    return WriteBatch(batch, true);
+    WriteBatch(batch, true);
+    return true;
 }
 
 bool BlockTreeDB::WriteFlag(const std::string& name, bool fValue)