BootControlAndroid::GetPartitionDevice ignore dynamic partitions

... on devices without dynamic partitions enabled. Previously,
we allowed to read target metadata even when dynamic partitions
are not enabled, because we planned a two-step OTA for retrofit
devices. This was needed at the second step when OTA client is
updated, dynamic partitions was not enabled, and target metadata
had just been written through InitPartitionMetadata.

Now that retrofit update is only one OTA, disable this.

Test: manual OTA
Bug: 118506262
Change-Id: Icbef61b0e42cb50bd7d1692580a48e082f512ddb