blockchain_import: Add --drop-hard-fork command

src/blockchain_db/berkeleydb/db_bdb.cpp

@@ -2192,6 +2192,11 @@ void BlockchainBDB::check_hard_fork_info()
 	/* FIXME: Some other time */
 }
 
+void BlockchainBDB::drop_hard_fork_info()
+{
+  /* TODO */
+}
+
 void BlockchainBDB::set_hard_fork_version(uint64_t height, uint8_t version)
 {
     LOG_PRINT_L3("BlockchainBDB::" << __func__);