ldb_tdb: Remove the idxptr DB before we re-index

ldb_tdb: Remove the idxptr DB before we re-index

We do not want the cache or any of the values in it, we want to read the real DB
@INDEX: records.

This matters if a re-index is tiggered in the same transaction
as the modify of the values in the index.  Otherwise we won't see
the old index record (it will not show up in the tdb_traverse)
and so fail to remove it.

That in turn can cause a spurious unqiue index violation.

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>