Fix code so that df_dat$data df is only the year, values, & subind

[BrittanyTroast-NOAA]

Right now calculations for other dataframes (pos, neg) are being done in that (data) df and ideally the data df would just have the simple data and not extraneous columns.

[BrendanTurley-NOAA]

I simplified the code to not include the extraneous columns in my ribbon-plot-dev branch. I also simplified the output to have a ribbon df and not both pos and neg dfs.