dix: Dequeue pending events on frozen device on removal

When a device is removed while still frozen, the events queued for that
device remain while the device itself is freed.

As a result, replaying the events will cause a use after free.

To avoid the issue, make sure to dequeue and free any pending events on
a frozen device when removed.

CVE-2025-26600, ZDI-CAN-25871

This vulnerability was discovered by:
Jan-Niklas Sohn working with Trend Micro Zero Day Initiative

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Part-of: <!1828>