db_lmdb: errors dropping hf starting height db on reset are not fatal

This db is now dropped unconditionally, so may or may not be there
in the first place.

src/blockchain_db/lmdb/db_lmdb.cpp

@@ -1242,8 +1242,7 @@ void BlockchainLMDB::reset()
     throw0(DB_ERROR(lmdb_error("Failed to drop m_output_amounts: ", result).c_str()));
   if (auto result = mdb_drop(txn, m_spent_keys, 0))
     throw0(DB_ERROR(lmdb_error("Failed to drop m_spent_keys: ", result).c_str()));
-  if (auto result = mdb_drop(txn, m_hf_starting_heights, 0))
-    throw0(DB_ERROR(lmdb_error("Failed to drop m_hf_starting_heights: ", result).c_str()));
+  (void)mdb_drop(txn, m_hf_starting_heights, 0); // this one is dropped in new code
   if (auto result = mdb_drop(txn, m_hf_versions, 0))
     throw0(DB_ERROR(lmdb_error("Failed to drop m_hf_versions: ", result).c_str()));
   if (auto result = mdb_drop(txn, m_properties, 0))