[ Miklos Vajna: The point of the change is that without this, part switching in
Calc does not work, as Calc does not invalidate everything after a part switch
(unlike Impress), and we suppose the right fix for this is to let the clients
throw away the tiles, rather than letting Calc send out invalidations, too. ]

Change-Id: Id368b955c54efb87ecf3d59278ddb5cdbb2e7856
Reviewed-on: https://gerrit.libreoffice.org/17267Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>