Bug 29778: Prevent orphan additional contents

Bug 29778: Prevent orphan additional contents

When deleting a content, only the main one (lang="default") is removed,
which leads to orphan contents in the DB that are still displayed on the
UI.

Test plan:
0. Don't apply this patch
1. Create some contents, translate them in different languages
2. Delete some of them
=> Note that they are still displayed on the UI and that the entries
with lang!="default" are still in the DB
3. Apply this patch
4. Repeat 1
5. Run updatedatabase
6. Delete from of the contents
=> Note that the orphan entries created before you applied the patch
have been removed and that the "delete" behaviour is now working
correnctly.

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>