Change: Display rail and road type speed limit text in yellow.

[PeterN]

Motivation / Problem

Railtype and roadtype NewGRFs used to be able to exploit string colour bleeding to influence the colour of the speed limit in the string.

Mostly they set it to yellow. Since string colour bleeding is no longer possible, this trick no longer works.

Description

Make the game display all rail and road type speed limit text in yellow, to continue the "tradition"...

Limitations

Not really necessary, but I had a stash lying around...

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 GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, game_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