typo
Improve our Dependent Subclause

When MySQL optimizes our UPDATE where id in (SELECT) it doesn't know
that the tables are linked, so it ends up walking and examining lots and
lots of rows.  Including the ObjectType column means that mysql can
easily examine 1 row using our existing ObjectCustomFieldValues2 index
and update immediately.

There is no longer a need to add upgrade specific indexes for OCFVs (the
transaction indexes still improve performance).
There's no need to sort the subselect

All this does is force mysql to sort (possibly filesort) and we really
don't care about the order when we're going to use it to feed an update
or delete.
Merge branch '3.0/2.9.0-upgrade-performance' into 3.0-trunk