Fix documentation about default mouse mode

When video playback is turned off, the default mouse mode has changed
from "uhid" to "disabled" in 2c25fd7a8082307da19645a690c31403903fbb1e.

Update the documentation accordingly.

Refs #5410 <https://github.com/Genymobile/scrcpy/issues/5410>
Refs #5542 <https://github.com/Genymobile/scrcpy/issues/5542>