fix: remove root wall from survivor bunker

[0Monet]

Purpose of change

Remove the root walls from the survivor's bunker, because this terrain should logically only be found in the Triffid grove.

Describe the solution

Remove root walls from ws_survivor_bunker_f-1.
Also moved "monstergroup" and "item_group" in ws_survivor_bunker.json to the appropriate JSON file.

Describe alternatives you've considered

none

Additional context

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