The elan driver always "deactivates" the device after a cpature run. We
can simplify the while internal state into a single "active" state and
rely on the image device driving this state machine correctly.
i.e.:
* We start a callibrate/capture/deactivate when we go into the
AWAIT_FINGER_ON state
* We only store the fact that we are active and want to deactivate
* We rely on the image device never going into the AWAIT_FINGER_ON
state without first waiting for the finger to be off (which implies
deactivation).
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