Changes

ccid_host: remove unused _set_dtr

Fix for:

cuart_driver_tty.c:62:13: warning: '_set_dtr' defined but not used [-Wunused-function]
   62 | static void _set_dtr(int fd, bool dtr)

Change-Id: I43b08a584891e94b9cfab095834e499dd5914b4f