innodb.row_format_redundant: Really corrupt the SYS_TABLES.MIX_LEN,
and do not use any debug instrumentation. For tables created in the
system tablespace, the contents of the column will be ignored.
Only the table t1 will refuse to load.

dict_load_table_one(): Remove the DBUG_EXECUTE_IF instrumentation.
Omit a redundant error message "incorrect flags in SYS_TABLES".

dict_sys_tables_rec_read(): Partially revert the Oracle Bug#21644827
fix, and always report errors by the return value.

fts_create_in_mem_aux_table(): Do not rely on dict_table_t::flags2,
but instead evaluate the tablespace ID.

DICT_TF2_BITS: Reduce to the correct value of 7. The two extra
high-order bits were specific to MySQL 5.7.