floss: Don't set the AdapterDiscoverableTimeout property

After https://r.android.com/3256460, we always set_discoverable when
powering off. This sets the AdapterDiscoverableTimeout property and
makes it always necessary to write the config onto the disk, causing the
"Stopping Module Storage Module timeout" issue again.

All that LibBluetooth does for the AdapterDiscoverableTimeout property
is writing it to the disk, and the real timeout handling is actually
done by the Rust layer.

Since Floss doesn't need this property to persist across power cycle,
NOT setting the property is safe and doesn't make anything functionality
change.

Bug: 310147428
Tag: #floss
Test: mmm packages/modules/Bluetooth
Test: Toggle BT, SaveImmediately is not called
Flag: EXEMPT, Floss-only changes
Change-Id: I3ea064b73a175e063ff89d059889d1fb404f9553