Fix 03cc0d6: Mark level crossings dirty when removing road from them, not from bridges

[2TallTyler]

Motivation / Problem

In 03cc0d6 / #9931 I introduced an assertion failure when removing road or tram from a shared bridge, reported as #10133.

When upstreaming the JGRPP implementation of this feature, I pasted a line of code into the wrong, but similar-looking place in RemoveRoad.

Instead of updating adjacent level crossings when removing road from a level crossing tile, it is done when removing road from a bridge tile.

Description

Put the code in the right place.

Closes #10133.

Limitations

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