Stop projecting threat zones from front lines.

This is an interim improvement since we should probably be pushing the
BARCAPs into TARCAP roles when the front line is so close. This does
regress flight pathing for anything that should route around the front
(to avoid getting shot at by SHORADS and TARCAPs), but for now it's one
or the other and this is the one everyone's complaining about.

(cherry picked from commit e474748f4d)

game/threatzones.py

@@ -152,23 +152,6 @@ class ThreatZones:
                         threat_zone = point.buffer(threat_range.meters)
                         air_defenses.append(threat_zone)
 
-        for front_line in game.theater.conflicts(player):
-            vector = Conflict.frontline_vector(
-                front_line.control_point_a, front_line.control_point_b, game.theater
-            )
-
-            start = vector[0]
-            end = vector[0].point_from_heading(vector[1], vector[2])
-
-            line = LineString(
-                [
-                    ShapelyPoint(start.x, start.y),
-                    ShapelyPoint(end.x, end.y),
-                ]
-            )
-            doctrine = game.faction_for(player).doctrine
-            air_threats.append(line.buffer(doctrine.cap_engagement_range.meters))
-
         return cls(
             airbases=unary_union(air_threats), air_defenses=unary_union(air_defenses)
         )