The prototype of matrix_output_unselect_delay() has been changed as follows.
```c
void matrix_output_unselect_delay(uint8_t line, bool key_pressed);
```
Currently, no keyboard seems to be redefining `matrix_output_unselect_delay()`, so there is no change in the system behavior.
With this change, the keyboard level code can get some optimization hints, for example, the following.
```c
void matrix_output_unselect_delay(uint8_t line, bool key_pressed) {
/* If none of the keys are pressed,
* there is no need to wait for time for the next line. */
if (key_pressed) {
#ifdef MATRIX_IO_DELAY
# if MATRIX_IO_DELAY > 0
wait_us(MATRIX_IO_DELAY);
# endif
#else
wait_us(30);
#endif
}
}
```
