Disallow squadrons from disabling mission types.

After this change, players will always have the final say in what
missions a squadron can be assigned to. Squadrons are not able to
influence the default auto-assignable missions either because that
property is always overridden by the campaign's air wing configuration
(the primary and secondary task properties). The `mission-types` field
of the squadron definition has been removed since it is no longer
capable of influencing anything. I haven't bothered cleaning up the now
useless data in all the existing squadrons though.

Fixes https://github.com/dcs-liberation/dcs_liberation/issues/2785.

game/squadrons/airwing.py

@@ -2,7 +2,7 @@ from __future__ import annotations
 
 import itertools
 from collections import defaultdict
-from typing import Sequence, Iterator, TYPE_CHECKING, Optional
+from typing import Iterator, Optional, Sequence, TYPE_CHECKING
 
 from game.ato.closestairfields import ObjectiveDistanceCache
 from game.dcs.aircrafttype import AircraftType

game/squadrons/squadrondef.py

@@ -1,8 +1,6 @@
 from __future__ import annotations
 
-import logging
-from collections.abc import Iterable
-from dataclasses import dataclass, field
+from dataclasses import dataclass
 from pathlib import Path
 from typing import Optional, TYPE_CHECKING
 
@@ -38,7 +36,6 @@ class SquadronDef:
 
     def capable_of(self, task: FlightType) -> bool:
         """Returns True if the squadron is capable of performing the given task.
-
         A squadron may be capable of performing a task even if it will not be
         automatically assigned to it.
         """