Duplicate tasks for daily mean fields

[ifenty]

In generating the tasks lists (or splitting the task lists), somehow we end up with a duplicate entry for the last daily mean file:

!Duplicates: [np.str_('s3://ecco-dataset-production-datasets/V4r5/latlon/day_mean/OCEAN_BOTTOM_PRESSURE/OCEAN_BOTTOM_PRESSURE_day_mean_2019-12-31_ECCO_V4r5_latlon_0p50deg.nc')]

@gjmoore