remove check check if all elements are ts like from db_ts_store.list

[HomoCodens]

• db_ts_store.tslist already has such a check
• if an empty list is passed to the .list variant this causes an error because sapply returns a list(), not a vector. the .tslist method avoids this by first checking if the list is empty

kof-internal note: this should fix the intermittent kofcast-dag failures