Information related to default metrics is outdated

[nikosbosse]

We previously had several places where we collected information about the default metrics in scoringutils:

• The metrics.rda and metrics-detailed.rds files (and the corresponding metrics data set
• The create-metric-tables.R script
• The Vignettes metric-details.Rmd and scoring-forecasts-directly.Rmd

This info should be deleted and eventually replaced by new information.