hal_p260c.c:  silence compiler warning
hal_p260c.c:  silence compiler warning

Comment out function, all of whose calls are commented out

Compiling realtime hal/drivers/hal_p260c.c
hal/drivers/hal_p260c.c:561:13: warning: 'flush_input' defined but not used [-Wunused-function]
 static void flush_input( int board )
             ^~~~~~~~~~~

strahlex/machinekit,strahlex/machinekit,strahlex/machinekit,strahlex/machinekit,strahlex/machinekit,strahlex/machinekit,strahlex/machinekit