RemoveCallback — Unregisters any callback registered for the given reason
$plot->RemoveCallback($reason)
RemoveCallback unregisters any callback registered
for the given reason.
It undoes the effect of SetCallback.
Returns True if the given reason is valid (whether or not there was actually a callback registered for it). Returns False if reason is not a valid callback reason.
Callbacks are an experimental feature added to PHPlot-5.0.4. Refer to Chapter 9, Callbacks for more information.