Fix JSON serialization issue in _get_crash_occurrence_platforms_from_crash_parameters (#1909)
Fix JSON serialization issue in _get_crash_occurrence_platforms_from_crash_parameters (#1909)

Memoize module caches result as json, so revert to using lists
than sets.
google/clusterfuzz,google/clusterfuzz,google/clusterfuzz,google/clusterfuzz,google/clusterfuzz,google/clusterfuzz,google/clusterfuzz,google/clusterfuzz