[server] Remove pseudo-handling of exceptions in Repository._delete_cascade_multi()
It seems to me that we never want to pass on an exception here be it in "test"
mode or not, so remove the last `except Exception:` clause. For instance, the
actual implementation would pass on an IntegrityError and thus possibly hide
it in a log message.
Concerning the `except Unauthorized:`, as said by the log message this should
not happen because we are within a `security_enabled(write=False)` context. So
remove it as well.
As far as I can tell, this strange handling of exceptions dates from
37668bf302f5 and there is no clear justification to it.