preventing StopLocations from propogating to one another during merge

[CaylaSavitzky]

Summary:

preventing StopLocations from propogating to one another during merge

StopLocations are the parent for Stop, Location, LocationGroup. Previously the merge either would cause these fields to propagate to eachother, or to keep the only the original fields in some deduplication strategies, but delete all three fields in other deduplication strategies

Expected behavior:

merged stoptimes should keep the same stop_id, location_id, and location_group_id values as before they were merged.

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