Remove the dataset indicator number from plots

[wpreimes]

The number prefix we have to make data set names unique can be confusing (in the results plots).

e.g 1-ERA5 (1 minus ERA5?)
Ideally those number are only used when multiple versions of the same dataset/version/variable are used. And then it should be called e.g. ERA5 (1) instead.

This affects ALL plots (maps, boxplots, metadata box plots etc.)