Destroy DE apex data snapshots when rollback is deleted.

This calls through to ApexService to destroy all the DE snapshots
for a rollback when that rollback is deleted.

Bug: 141148175
Test: Install APEX with rollback enabled, expire rollback and check snapshot
has been deleted.
Change-Id: I8a8d3d89f7570a55b4a516376bad311a61d637ec