Deprecate `ComputerControlSession.getAccessibilityWindows()`.

The `getAccessibilityWindows()` method is no longer in use. This change marks it as deprecated and modifies it to return an empty list.

Test: Bonobo app still works
Flag: android.companion.virtualdevice.flags.computer_control_access
Bug: 437852886
Change-Id: I2633f18accf5a0952f0aa63b4207628ad55714c6