don't delete build events from child partitions
don't delete build events from child partitions

there was a slight flaw in this migration

Signed-off-by: Corbin Halliwill <38cf05332854d0c00b392ad9da3fb5cec295aa83@pivotal.io>

zachgersh/atc,zachgersh/atc,zachgersh/atc,zachgersh/atc