[server] Don't destroy SlideInterface when parent SurfaceInterface is destroyed
Summary:
Destroying the SlideInterface on the server side before the client has a
chance to cleanup results in a protocol error:
wl_display@1: error 0: invalid object 7
Which would terminate the client. If we would not destroy the resource,
but only delete the SlideInterface it could result in heap-use-after-free.
So just don't do anything, the client needs to cleanup which will result
in the SlideInterface being deleted.
Reviewers: Plasma
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D1714