Description

After #9725, cmd_helper is almost useless.

The few remaining IsEnumValid() can be replaced with IsValidDirection(), IsValidAxis...
The few remaining Extract<>() in story.cpp can also be replaced.

Limitations

I don't know if there is any plan of using these again, but probably they won't.

If there is no need of keeping Extract, IsEnumValid and cmd_helper.h, it is also possible to remove EnumPropsT.

If developers think so, just say it and I will remove EnumPropsT related code in another commit to this same PR.

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR touches english.txt or translations? Check the guidelines
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, gs_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker