SpikeSortingOutput calls non-existent method

[CBroz1]

#807 edited SpikeSortingOutput.get_spike_indicator to call cls.fetch_spike_data here

This function exists as part of SortedSpikesGroup, but not SpikeSortingOutput or any part-parents.

get_firing_rate also relies on get_spike_indicator. Should we implement the dependency or remove these methods?

[samuelbray32]

I think the call just needs to be changed to SpikeSortingOutput().get_spike_times(key)