viaUnregisterPreViaEngineCallback

viaUnregisterPreViaEngineCallback(
)
=> t / nil

Unregisters the preViaEngine procedure if it has been registered. If it has not been registered, this function does nothing.

None

`t`	Returns `t` if the function is successfully unregistered.
`nil`	Returns `nil` if the function is not successfully unregistered.

viaUnregisterPreViaEngineCallback()