feat(uart): only enable on_receive task if necessary

The onReceive Task was created by default when Serial.begin() is executed. This creates a additonal Task that degrades the performance of the whole arduino sketch.

This will be done now only if onReceive() is called.

cores/esp32/HardwareSerial.cpp

@@ -368,11 +368,6 @@ void HardwareSerial::begin(unsigned long baud, uint32_t config, int8_t rxPin, in
       _uart = NULL;
     }
   }
-  // create a task to deal with Serial Events when, for example, calling begin() twice to change the baudrate,
-  // or when setting the callback before calling begin()
-  if (_uart != NULL && (_onReceiveCB != NULL || _onReceiveErrorCB != NULL) && _eventTask == NULL) {
-    _createEventTask(this);
-  }
 
   // Set UART RX timeout
   uartSetRxTimeout(_uart, _rxTimeout);