When deleting one database, all the tables, including the ones stored in the recycle bin, it has should be deleted first, otherwise the error will be popped up.
curl -u shiva:shiva -XDELETE 'localhost:8902/hippo/v1/_database?pretty' -H 'Content-Type: application/json' -d'{
"database_name" : "book"
}';
Result:
{
"acknowledged" : true
}