Issue #765 - Delete old overviews of the default metrics

[nikosbosse]

Description

This PR closes #765.
This PR closes #757.

As discussed in #764, the old information on the default metrics is outdated. This PR deletes this information. I'll add new info in a new PR (#762).

The PR

• Deletes the metrics.rda and metrics-detailed.rds files (and the corresponding metrics data set
• Deletes the create-metric-tables.R script
• Deletes the Vignettes metric-details.Rmd and scoring-forecasts-directly.Rmd
• Deletes a call to the metrics data from the scoringutils.Rmd Vignette
• has unintentional(!) unrelated changes: some .Rd docs files got updates when I reinstalled the package (I think that's related to a suggested change during the last PR where we only changed the .R file, not the .Rd file)

Checklist

• My PR is based on a package issue and I have explicitly linked it.
• I have included the target issue or issues in the PR title as follows: issue-number: PR title
• I have tested my changes locally.
• I have added or updated unit tests where necessary.
• I have updated the documentation if required.
• I have built the package locally and run rebuilt docs using roxygen2.
• My code follows the established coding standards and I have run lintr::lint_package() to check for style issues introduced by my changes.
• I have added a news item linked to this PR.
• I have reviewed CI checks for this PR and addressed them as far as I am able.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.29%. Comparing base (9f11180) to head (ce416d8).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #764   +/-   ##
=======================================
  Coverage   95.29%   95.29%           
=======================================
  Files          21       21           
  Lines        1594     1594           
=======================================
  Hits         1519     1519           
  Misses         75       75           

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