Purchase reserves at front lines.

This changes the ground unit purchase behavior such that the supply
limit is exceeded by 30%, with the extra units kept in reserve.

The old hard cap of 50 units is no longer needed, since the ammo supply
now does the same task, so that's been removed.

game/settings.py

@@ -57,7 +57,6 @@ class Settings:
     perf_moving_units: bool = True
     perf_infantry: bool = True
     perf_destroyed_units: bool = True
-    front_line_procurement_target: int = 50
     reserves_procurement_target: int = 10
 
     # Performance culling