Remove old check_db_name() from make_table_name_list()

  if (check_db_name((LEX_STRING*)db_name))

     return 0; // Impossible TABLE_SCHEMA name

  DBNameBuffer dbbuf(*db_name, lower_case_table_names);

  const Lex_ident_db dbnorm= dbbuf.to_lex_ident_db();

  if (!dbnorm.str)

     return 0; // Impossible TABLE_SCHEMA name

int ha_discover_table_names(THD *thd, const LEX_CSTRING *db, MY_DIR *dirp,

                            Discovered_table_list *result, bool reusable);

struct handlerton

{

  ...

  int (*discover_table_names)(handlerton *hton, const LEX_CSTRING *db,

                              MY_DIR *dir,

                              discovered_list *result);

  ...

};