fix: description and id of t_thconc_floor_nofloor

[0Monet]

Purpose of change

Redo #3891.
Change description and id of t_thconc_floor_nofloor.

Describe the solution

Remove t_thconc_floor_nofloor from acidia_commercial_destroyed_palette.json
Create t_thconc_floor_no_roof with t_thconc_floor_nofloor as "alias" in terrain-floors-outdoors.json

Describe alternatives you've considered

Change only the description.

Testing

1. Took a save file made before these changes.
2. Load the save file in another game, which contains these changes in the JSON.
3. No errors.

Additional context

none

[chaosvolt]

Tested that the alias works as intended in old saves with the old terrain kicking around, seems to be all good.

[scarf005]

merging as the tests all pass.