Remove uart emulation

which is not maintained (and not functional) and will
be replaced by an official SoftwareSerial port.
See stm32duino#267.

Signed-off-by: Frederic.Pillon <frederic.pillon@st.com>

Author: fpistm

cores/arduino/board.h

@@ -12,7 +12,6 @@ extern "C"{
 #include "clock.h"
 #include "core_callback.h"
 #include "digital_io.h"
-#include "hal_uart_emul.h"
 #include "hw_config.h"
 #include "low_power.h"
 #include "rtc.h"
@@ -21,7 +20,6 @@ extern "C"{
 #include "timer.h"
 #include "twi.h"
 #include "uart.h"
-#include "uart_emul.h"
 #ifdef USBCON
 #include "usb_interface.h"
 #endif //USBCON