wlr_input_device: fix keyboard destruction
wlr_input_device: fix keyboard destruction

After destroying a keyboard input device, seat's listeners could still be pointing to destroyed wlr_input_device signals. This patch makes sure the references are removed while the input device is being destroyed.

ascent12/wlroots,ascent12/wlroots,swaywm/wlroots,SirCmpwn/wlroots,swaywm/wlroots