V547 Expression 'mpTargetSlideSorter != nullptr' is always false.

The code wasn't used since commit 4b83a7fe
(initially, mpTargetSlideSorter pointer was compared to a pSlideSorter
parameter, which was always nullptr since commit above; then commit
f946e905 removed the const parameter).

Change-Id: I70047ae3e7ef39419be0012e375856d8a50d5793
Reviewed-on: https://gerrit.libreoffice.org/63229
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>