disable BT Serial examples for S2

libraries/BluetoothSerial/examples/SerialToSerialBT/SerialToSerialBT.ino

@@ -3,6 +3,7 @@
 //
 //This example creates a bridge between Serial and Classical Bluetooth (SPP)
 //and also demonstrate that SerialBT have the same functionalities of a normal Serial
+#if CONFIG_IDF_TARGET_ESP32
 
 #include "BluetoothSerial.h"
 
@@ -26,4 +27,8 @@ void loop() {
     Serial.write(SerialBT.read());
   }
   delay(20);
-}
+}
+#else
+void setup() {}
+void loop() {}
+#endif