Remove shadowing member variables

- The variables shadow SerialBase::_tx_enabled and SerialBase::_rx_enabled

Author: Sebastian Stockhammer

drivers/UARTSerial.h

@@ -296,8 +296,6 @@ class UARTSerial : private SerialBase, public FileHandle, private NonCopyable<UA
     bool _blocking;
     bool _tx_irq_enabled;
     bool _rx_irq_enabled;
-    bool _tx_enabled;
-    bool _rx_enabled;
     InterruptIn *_dcd_irq;
 
     /** Device Hanged up

drivers/source/UARTSerial.cpp

@@ -28,8 +28,6 @@ UARTSerial::UARTSerial(PinName tx, PinName rx, int baud) :
     _blocking(true),
     _tx_irq_enabled(false),
     _rx_irq_enabled(false),
-    _tx_enabled(true),
-    _rx_enabled(true),
     _dcd_irq(NULL)
 {
     /* Attatch IRQ routines to the serial device. */
@@ -41,8 +39,6 @@ UARTSerial::UARTSerial(const serial_pinmap_t &static_pinmap, int baud) :
     _blocking(true),
     _tx_irq_enabled(false),
     _rx_irq_enabled(false),
-    _tx_enabled(true),
-    _rx_enabled(true),
     _dcd_irq(NULL)
 {
     /* Attatch IRQ routines to the serial device. */