native: removed dead code

num was never read, because native will exit before.

cpu/native/periph/random.c

@@ -92,7 +92,6 @@ int random_read(char *buf, unsigned int num)
             num = _native_rng_read_det(buf, num);
             break;
         default:
-            num = 0;
             err(EXIT_FAILURE, "random_read: _native_rng_mode is in invalid state %i\n",
                    _native_rng_mode);
             break;