seat: Let client manage its own resources

This makes seat_client resources inert when seats and/or input devices are
destroyed, rather than destroying the resources.

When the client calls e.g. wl_keyboard_release(), it's not expecting the
keyboard global to be already destroyed, so this results in an error such
as this:

    wl_display@1: error 0: invalid object 22

0 files changed, 0 insertions, 0 deletions