Remove the enemy forces multiplier option.

This didn't do what it claimed to (it actually just determines the
threshold for whether a control point shoudl be a *preferred* canidate
for purchasing ground units), and the income multipliers offer the
intended behavior.

game/settings.py

@@ -17,7 +17,6 @@ class Settings:
     night_disabled: bool = False
     external_views_allowed: bool = True
     supercarrier: bool = False
-    multiplier: float = 1.0
     generate_marks: bool = True
     manpads: bool = True
     cold_start: bool = False  # Legacy parameter do not use