Revert "Disable STDIN input to allow deepsleep"

This reverts commit ec9a6a3.
It had no effect on low power, on the contrary was preventing a correct functionality on Nano 33 BLE UART pins used as GPIOs.

Author: giulcioffi

cores/arduino/main.cpp

@@ -36,9 +36,6 @@ int main(void)
 	init();
 	initVariant();
 
-	// we are never going to use getchar/scanf directly
-	mbed::mbed_file_handle(STDIN_FILENO)->enable_input(false);
-
 #if defined(SERIAL_CDC)
   PluggableUSBD().begin();
   _SerialUSB.begin(115200);