correctly dispose to avoid cyclic dependencies

accessibility cruft is still listening to dead tables so crashes in
slidesorting in main panel if moved slide has tables in it after visiting slide
sorter once.

(cherry picked from commit 0b8e2e5efe20519e8b5563314bac0cbb84a3b967)

Conflicts:
	svx/source/table/svdotable.cxx

Change-Id: I09f9a73b01fb2ddf059402146acdc7bd823798b9
Reviewed-on: https://gerrit.libreoffice.org/7051
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>