Revert "Fixes #1709 - Cannot create Launch Configuration with Block Device Mappings"

This worked correctly for AutoScaling, but broke EC2. A modified patch
will land shortly.
This reverts commit 5fd728e8464b40b91a8e25058e1b828853f5cb43.
Test exposes AutoScaling ``launch_configuration`` bug when using block device mappings.
Fixes #1723 - A prior commit broke ``run_instances`` with block device mappings on EC2. This makes both EC2 & Autoscaling work with block device mappings.