[t:4695], fix compilation issue

git-svn-id: file:///svn/mysql/tokudb-engine/tokudb-engine@41780 c7de825b-a66e-492c-adef-691d508d4ae1

storage/tokudb/ha_tokudb.cc

@@ -7752,7 +7752,6 @@ int ha_tokudb::final_add_index(handler_add_index *add_arg, bool commit) {
 
     // extract the saved state variables
     ha_tokudb_add_index *add = static_cast<class ha_tokudb_add_index*>(add_arg);
-    DB_TXN *txn = add->txn;
     bool incremented_numDBs = add->incremented_numDBs;
     bool modified_DBs = add->modified_DBs;
     TABLE *table = add->table;