Fix the CSV file generation of bench_download script

[Akirathan]

Pull Request Description

One can now once more create CSV files from benchmark results with something like:

./bench_download.py -v -s stdlib --since 2024-01-01 --create-csv

The generated CSV is ready to be read by the Enso IDE.

Important Notes

• Fix --create-csv functionality of the bench_download.py script.
• Remove an outdated Enso project from tools/performance/engine_benchmarks/Engine_Benchs
  • This is now done by book clubs.

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• Screenshots/screencasts have been attached, if there are any visual changes. For interactive or animated visual changes, a screencast is preferred.
• All code follows the
  Scala,
  Java,
  and
  Rust
  style guides. In case you are using a language not listed above, follow the Rust style guide.
• All code has been tested:
  • Unit tests have been written where possible.
  • If GUI codebase was changed, the GUI was tested when built using ./run ide build.