Some Features Removed from Fork

- Set CultureInfo in Configuration: Have been done in the meantime by
Josh Close

- SetConstantValue: Can be solved via "ConvertUsing" (see new
"ConvertUsingConstantTest" in the source repository)

- Origin Reader and SpeedTest between new and old one removed. Basic
modification was merged to main repo
(https://github.com/JoshClose/CsvHelper/commit/1455a5408959d30cdb8b98a03687fce36878ad1d)