get rid of last use of UniString in LibreOffice

of raw "UniString" :-), the rest use the #define UniString String alias

Change-Id: I6c4ca3a6c2b425b9214691e03deda5dd1a8a11bf

svx/source/svdraw/svdundo.cxx

@@ -255,9 +255,9 @@ void SdrUndoAttrObj::ensureStyleSheetInStyleSheetPool(SfxStyleSheetBasePool& rSt
     {
         // re-insert remembered style which was removed in the meantime. To do this
         // without assertion, do it without parent and set parent after insertion
-        const UniString aParent(rSheet.GetParent());
+        const OUString aParent(rSheet.GetParent());
 
-        rSheet.SetParent(UniString());
+        rSheet.SetParent(OUString());
         rStyleSheetPool.Insert(&rSheet);
         rSheet.SetParent(aParent);
     }