Do not _RemoveDisks after failed _CreateDisks

Now that _CreateDisks cleans up after itself in case of failure,
do not clean up at call sites, as there we have to overapproximate
thus potentially causing data loss.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>