Fix external libraries, requires Flatpak migration

In favor of fixing external steam library support, drop support for
having an ammo.conf specific to Flatpak and another ammo.conf specific
to Steam in cases where a game was installed in both locations.

Instead, only use the normal ~/.local/share/ammo/<game name>/ammo.conf,
and show the library location on the game selection screen. This is more
accurate since it's possible to use Flatpak steam to add an external
library, at which point there's no way to tell that external library was
accessed via Flatpak steam. Steam installation instances do not have
exclusive ownership of steam libraries.

If you had games installed via Flatpak, pulling this update will
require you to either reactivate/reorder your mods and commit, or move
~/.var/app/com.valvesoftware.Steam/.local/share/ammo to
~/.local/share/ammo.

ammo/game_controller.py

@@ -17,16 +17,9 @@
 )
 
 
-class Source(str, Enum):
-    UNKNOWN = "unknown"
-    STEAM = "steam"
-    FLATPAK = "flatpak"
-
-
 @dataclass(frozen=True, kw_only=True)
 class GameSelection:
     name: field(default_factory=str)
-    source: field(default_factory=Source)
     library: field(default_factory=Path)
 
 
@@ -80,15 +73,8 @@ def __init__(self):
                     if game.name not in self.ids:
                         continue
 
-                    source = Source.UNKNOWN
-                    if self.steam in [library, library.parents]:
-                        source = Source.STEAM
-                    elif self.flatpak in [library, library.parents]:
-                        source = Source.FLATPAK
-
                     game_selection = GameSelection(
                         name=game.name,
-                        source=source,
                         library=library,
                     )
 
@@ -116,7 +102,7 @@ def __str__(self) -> str:
         result += "-------|-----\n"
         for i, game in enumerate(self.games):
             index = f"[{i}]"
-            result += f"{index:<7} {game.name} ({game.source.value})\n"
+            result += f"{index:<7} {game.name} ({game.library})\n"
         return result
 
     def _autocomplete(self, text: str, state: int) -> Union[str, None]:
@@ -152,17 +138,8 @@ def _manage_game(self, index: int) -> None:
             app_data / f"{game_selection.name.replace('t 4', 't4')}/Plugins.txt"
         )
         data = directory / "Data"
-        if game_selection.source == Source.FLATPAK:
-            ammo_conf_dir = (
-                Path.home()
-                / f".var/app/com.valvesoftware.Steam/.local/share/ammo/{game_selection.name}"
-            )
-        elif game_selection.source == Source.STEAM:
-            ammo_conf_dir = Path.home() / f".local/share/ammo/{game_selection.name}"
-        else:
-            raise TypeError(
-                f"Expected {list(Source)} but got {game_selection.source} of type {type(game_selection.source)}"
-            )
+
+        ammo_conf_dir = Path.home() / f".local/share/ammo/{game_selection.name}"
         ammo_mods_dir = ammo_conf_dir / "mods"
         ammo_conf = ammo_conf_dir / "ammo.conf"