Clear loaded scenario blacklist when leaving world

[anothersimulacrum]

Summary

SUMMARY: None

Purpose of change

Fixes #37892
This caused you to be unable to load a world with a mod containing a scenario blacklist more than once without exiting the game.

Also don't locally redefine all_scenarios when finalizing scenario blacklists.

Describe the solution

Reset the scenario blacklist when unloading data.

Testing

I am able to load a world with this mod more than once without exiting the game.

[
  {
    "type": "MOD_INFO",
    "ident": "scenmod",
    "name": "No scenarios!",
    "authors": [ "anothersimulacrum" ],
    "maintainers": [ "you" ],
    "description": "Tests scenario blacklists",
    "dependencies": [ "dda" ]
  },
  {
    "type": "SCENARIO_BLACKLIST",
    "subtype": "whitelist",
    "scenarios": [ "largebuilding" ]
  }
]