Copter: reorder beacon and proximity declaration

resolves compiler warning

ArduCopter/Parameters.h

@@ -565,14 +565,14 @@ public:
     // ground effect compensation enable/disable
     AP_Int8 gndeffect_comp_enabled;
 
+    // beacon (non-GPS positioning) library
+    AP_Beacon beacon;
+
 #if PROXIMITY_ENABLED == ENABLED
     // proximity (aka object avoidance) library
     AP_Proximity proximity;
 #endif
 
-    // beacon (non-GPS positioning) library
-    AP_Beacon beacon;
-
     // whether to enforce acceptance of packets only from sysid_my_gcs
     AP_Int8 sysid_enforce;