Update secondary indexes using DataUpdateClosure.

This removes EntityModificationUpdate and related classes
and provides a more flexible way to define data updates to
be applied when modifying or deleting entities.

This allows us to introduce the neccessary data updates for
redirects more easily.

Bug: 66028
Change-Id: I6afd88baea840f9fedfd558b29d45889fb01584c
Merge "Update secondary indexes using DataUpdateClosure."