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As the massive edit on deleted computers isn't available, here is the SQL command to change status of all deleted computers: 

UPDATE glpi_computers SET states_id=#id_of_wanted_state# WHERE is_deleted=1;

The feature exist since version 10.0.0 in automatic actions, disabled by default. However, this feature does not remove versions and softwares that are attached to computers in the trashbin. It will be nice to have an option to delete these versions as well.