disposed but not dtored

just die when you are supposed to, without this endless amounts of accessiblity
cells remain after sorting slides with tables in them

(cherry picked from commit 1c28065d8fe3e9a1394a7ecfc29e95a9639a1012)

Conflicts:
	svx/source/table/accessibletableshape.cxx

Change-Id: Ice9a86b8b806e58f9bf871341a38f7729798dda9
(cherry picked from commit a90e08cb15e712e1d15a16de9a2677e57d81fd13)
Reviewed-on: https://gerrit.libreoffice.org/7052
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>