fix crash on pdf import of fdo30892-1

after
    commit a9ef9437
    Date:   Wed Feb 28 11:09:43 2018 +0200
    loplugin:useuniqueptr in sdext

Change-Id: I964e2319d583455c2c698f895e0b675d69256e38
Reviewed-on: https://gerrit.libreoffice.org/51475Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

sdext/source/pdfimport/tree/drawtreevisiting.cxx

@@ -736,7 +736,6 @@ void DrawXmlOptimizer::optimizeTextElements(Element& rParent)
                     pCur->Children.splice( pCur->Children.end(), pNext->Children );
                     // get rid of the now useless element
                     rParent.Children.erase( next );
-                    delete pNext;
                     bConcat = true;
                 }
             }