gpui: Drop unnecessary use of `StringIndexConverter` (#41221)

Might help with ZED-1FF

Release Notes:

- N/A *or* Added/Fixed/Improved ...
95ad7a6caeLukas Wirth committed on 10/26/2025, 10:35:33 AM· committed by GitHubparent54a7da3
1 file changedLine totals unavailable