'Remove the trigger if it has yet to be executed, otherwise emit a
warning that in the future an exception will be raised when removing an
already-executed trigger.
@see: removeTrigger'

def removeTrigger_BEFORE(self, handle):

    (phase, callable, args, kwargs) = handle
    if (phase != 'before'):
        return self.removeTrigger_BASE(handle)
    if ((callable, args, kwargs) in self.finishedBefore):
        warnings.warn('Removing    already-fired    system    event    triggers    will    raise    an    exception    in    a    future    version    of    Twisted.', category=DeprecationWarning, stacklevel=3)
    else:
        self.removeTrigger_BASE(handle)
