Remove obsolete comments

- The corresponding section is called from multiple locations now

Author: Sebastian Stockhammer

drivers/source/UARTSerial.cpp

@@ -339,7 +339,7 @@ void UARTSerial::update_rx_irq()
 {
     core_util_critical_section_enter();
     if (_rx_enabled && !_rx_irq_enabled) {
-        UARTSerial::rx_irq();               // only read from hardware in one place
+        UARTSerial::rx_irq();
         if (!_rxbuf.full()) {
             SerialBase::attach(callback(this, &UARTSerial::rx_irq), RxIrq);
             _rx_irq_enabled = true;
@@ -358,7 +358,7 @@ void UARTSerial::update_tx_irq()
 {
     core_util_critical_section_enter();
     if (_tx_enabled && !_tx_irq_enabled) {
-        UARTSerial::tx_irq();                // only write to hardware in one place
+        UARTSerial::tx_irq();
         if (!_txbuf.empty()) {
             SerialBase::attach(callback(this, &UARTSerial::tx_irq), TxIrq);
             _tx_irq_enabled = true;