Remove schematic upgrades and module and ship levels

src/balancing/ArenaSimulation.h

@@ -3,6 +3,7 @@
 #include <atomic>
 #include <memory>
 #include <mutex>
+#include <optional>
 #include <random>
 #include <string>
 #include <vector>
@@ -32,7 +33,9 @@ struct ArenaStatus
     struct Entry
     {
         std::string displayName;
-        int level;
+        // Level suffix shown in the widget/inspect display. Set for the HQ and
+        // defence stations; empty for ships, which no longer have a level.
+        std::optional<int> level;
         int total;
         int surviving;
     };