[deployments] Restore DELETE /deployments/devices/{id}

We moved this endpoint from management to internal, because it is part of the decommissioning workflow. This breaks API back-compatibility, though, and one of our customers reported it.

We decided to implement the end-point again, in the proper way:

• Mark all pending device deployments as "aborted"
• Loop over active deployments (static and dynamic) and, if the device matches, mark the device deployment as "aborted"