Deleted/moved articles are still present in (custom) selections

It looks like we do not correctly filter out deleted/moved articles from (custom) selections.

For instance, http://download.openzim.org/wp1/enwiki/customs/medicine.tsv list still contain `ARO-APOC3`while it seems to be delete since "quite a long ago".

I don't know if this is a problem specific to custom selections or a generic one.
