What's your definition of a duplicate in a table that has no (logical) primary key? Do yo mean that all your columns will have the same value? In such case, there's even no solution in standard SQL:
delete from table where <column1> = <value1> and <column2> = <value2> and ...
will always delete both duplicate records when the condition holds true.
You will need to revert to an internal concept like "$rowid$" in HANA to distinguish between both records and achieve your desired result.