This virtual operation is issued for a very particular event: the hardfork 23 that happened when the Hive blockchain split from Steem. At this time, several accounts have not been airdropped with HIVE tokens, so their existing delegations were instantly removed.
However, there were no operations of type delegate_vesting_share relating to this. It was recorded in the blockchain with hardfork_hive virtual operations, stored in the VOHardforkHives table.