vitals_hourly_data includes lots of duplicates

[juliangilbey]

When calculating numerics, the mimic_direct_extract.py main function pulls in data from both chartevents and labevents, but lots of these are duplicates. For example, there are 7 different itemids for White blood cell count, and lots of the data recorded is duplicated in both original spreadsheets (as described in the MIMIC documentation). So these duplicates should be removed before computing things such as count, mean and standard deviation for outputting to the vitals_hourly_data.