From what I recall, there is no combined "decrypt and uninstall" command. The only scriptable options are for the MSI installers, not for SEE's operation.
As far as decyption goes, the managed method is to assign a policy to the machines, forcing them to decrypt. This has the benefit of centralised management so you can be certain it has completed before pushing out a script for the uninstall (remove full disk/remoaveble storage first, then framework client).
Other methods to decrypt the drive (as I'm sure you're aware) are locally via the client console, or using the SEE Boot Images...
The fastest option of all (assuming all user data is stored in a centralised location and not on the endpoints themselves) is to just reimage the machine.