SERIAL_STATS_* features not supported on USBCON targets (#9127)

Marlin/src/gcode/queue.cpp

         card.closefile();
         SERIAL_PROTOCOLLNPGM(MSG_FILE_SAVED);
 
-        #if ENABLED(SERIAL_STATS_DROPPED_RX)
-          SERIAL_ECHOLNPAIR("Dropped bytes: ", customizedSerial.dropped());
-        #endif
+        #ifndef USBCON
+          #if ENABLED(SERIAL_STATS_DROPPED_RX)
+            SERIAL_ECHOLNPAIR("Dropped bytes: ", customizedSerial.dropped());
+          #endif
 
-        #if ENABLED(SERIAL_STATS_MAX_RX_QUEUED)
-          SERIAL_ECHOLNPAIR("Max RX Queue Size: ", customizedSerial.rxMaxEnqueued());
-        #endif
+          #if ENABLED(SERIAL_STATS_MAX_RX_QUEUED)
+            SERIAL_ECHOLNPAIR("Max RX Queue Size: ", customizedSerial.rxMaxEnqueued());
+          #endif
+        #endif // !USBCON
 
         ok_to_send();
       }

Marlin/src/inc/SanityCheck.h

   #elif TX_BUFFER_SIZE && (TX_BUFFER_SIZE < 2 || TX_BUFFER_SIZE > 256 || !IS_POWER_OF_2(TX_BUFFER_SIZE))
     #error "TX_BUFFER_SIZE must be 0, a power of 2 greater than 1, and no greater than 256."
   #endif
-#elif ENABLED(SERIAL_XON_XOFF)
-  #error "SERIAL_XON_XOFF is not supported on USB-native AVR devices."
+#elif ENABLED(SERIAL_XON_XOFF) || ENABLED(SERIAL_STATS_MAX_RX_QUEUED) || ENABLED(SERIAL_STATS_DROPPED_RX)
+  #error "SERIAL_XON_XOFF and SERIAL_STATS_* features not supported on USB-native AVR devices."
 #endif
 
 /**