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Aim of this patch is to remove tdc_remove_table(TDC_RT_REMOVE_UNUSED),
which was mistakenly introduced by 055a3334.

InnoDB allows only one open TABLE instance while performing table
truncation. To fulfill this requirement:
1. MDL_EXCLUSIVE has to be acquired to block concurrent threads from
   accessing given table
2. cached TABLE instances have to be flushed
3. another InnoDB requirement is such that TABLE_SHARE and remaining
   TABLE instance have to be invalidated and re-opened after truncation

This goes more or less inline with what regular TRUNCATE TABLE does.

Alternative solution would be handler::ha_delete_all_rows(), but InnoDB
doesn't implement it unfortunately.

Part of MDEV-17882 - Cleanup refresh version