lei/store: cull redundant docids based on blob OID

lei/store: cull redundant docids based on blob OID

I'm not sure how this happened (only once for me in March), but
it should not happen...  In any case, we'll operate on the
lowest numbered docid and cull redundant index entries when
lei/store is open for read-write.

This also fixes the normal lei/store removal path to clean up
the xref3 table (since it's not done automatically for
public-facing -eidx due to the multi-list nature of it).