Remove prop_damage from islot_ammo (#39600)

src/item_factory.cpp

@@ -1489,7 +1489,6 @@ void Item_factory::load( islot_ammo &slot, const JsonObject &jo, const std::stri
     assign( jo, "count", slot.def_charges, strict, 1 );
     assign( jo, "loudness", slot.loudness, strict, 0 );
     assign( jo, "effects", slot.ammo_effects, strict );
-    assign( jo, "prop_damage", slot.prop_damage, strict );
     assign( jo, "critical_multiplier", slot.critical_multiplier, strict );
     assign( jo, "show_stats", slot.force_stat_display, strict );
 }

src/itype.h

@@ -710,19 +710,13 @@ struct islot_ammo : common_ranged_data {
      * */
     bool special_cookoff = false;
 
-    /**
-     * If set, ammo does not give a flat damage, instead it multiplies the base
-     * damage of the gun by this value.
-     */
-    cata::optional<float> prop_damage;
-
     /**
      * The damage multiplier to apply after a critical hit.
      */
     float critical_multiplier = 2.0;
 
     /**
-     * Some combat ammo might not have a damage or prop_damage value
+     * Some combat ammo might not have a damage value
      * Set this to make it show as combat ammo anyway
      */
     cata::optional<bool> force_stat_display;