Automation Controls (and controls in general) are now
only updated in realtime context. Either via automation-playback,
or via SessioEvent. This directly sets the Control:_user_value
(before emitting the Changed signal).
The GUI does not need to evaluate the control at a given point
in time, so the API call can be removed and unified.
This commit first removes all calls to "get_double" to ensure
that no special cases exist.
a4a241c738