comment from sberg:
  aren't these changes broken in general, when the called function
  may throw an exception before it takes ownership of the passed-in pointer?

So revert, except for
  (a) PlainTextFilterDetect::detect, which was definitely a leak
  (b) SwCursor::FindAll, where unique_ptr was being unnecessarily used

This reverts commit 7764ae70.

Change-Id: I555e651b44e245b031729013d2ce88d26e8a357e
Reviewed-on: https://gerrit.libreoffice.org/60301Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Tested-by: Noel Grandin <noel.grandin@collabora.co.uk>