Move HardFork DB update to BlockchainDB::add_block()

Ensures the database is consistent.

Also simplifes blockchain_import in that verify mode off has less to
work around.

src/blockchain_utilities/blockchain_import.cpp

@@ -469,9 +469,6 @@ int import_from_file(FakeCore& simple_core, const std::string& import_file_path,
           try
           {
             simple_core.add_block(b, block_size, cumulative_difficulty, coins_generated, txs);
-            #if !defined(BLOCKCHAIN_DB) || (BLOCKCHAIN_DB == DB_LMDB)
-            simple_core.m_hardfork->add(b, h-1);
-            #endif
           }
           catch (const std::exception& e)
           {