sars-cov-2-origins/huanan-market: Correction of three files with median distances to the Huanan market

Correction of the 'distance_popdensityagegroups_null_35.csv' and 'distance_popdensityagegroups_null_120.csv' files that were identical to each other. Also 'distance_popdensityagegroups_null_155.csv' was updated to contain n = 1,000 distance used for all related analyses instead of n = 10,000.