m68k/atari: atakeyb.c - Remove some unused functions
Remove some functions that are not used anywhere:
atari_kbd_leds() ikbd_exec() ikbd_mem_read() ikbd_mem_write()
ikbd_clock_get() ikbd_clock_set() ikbd_pause() ikbd_resume()
This was partially found by using a static code analysis program called
cppcheck.