Copter: fix PRX_ parameters duplicate underscore in param name

ArduCopter/Parameters.cpp

@@ -1010,12 +1010,11 @@ const AP_Param::GroupInfo ParametersG2::var_info[] = {
     AP_GROUPINFO("DEV_OPTIONS", 7, ParametersG2, dev_options, 0),
 
 #if PROXIMITY_ENABLED == ENABLED
-    // @Group: PRX_
+    // @Group: PRX
     // @Path: ../libraries/AP_Proximity/AP_Proximity.cpp
-    AP_SUBGROUPINFO(proximity, "PRX_", 8, ParametersG2, AP_Proximity),
+    AP_SUBGROUPINFO(proximity, "PRX", 8, ParametersG2, AP_Proximity),
 #endif
 
-
     // @Param: ACRO_Y_EXPO
     // @DisplayName: Acro Yaw Expo
     // @Description: Acro yaw expo to allow faster rotation when stick at edges