Revert "-Werror,-Wunused-const-variable"

Actually used with follow-up commit
b94de8fa

This reverts commit e24a02dc.

Change-Id: I0f8226f756c7b3a813600351cc1be9bbbbcf67c2

xmloff/source/text/txtfldi.cxx

@@ -138,6 +138,7 @@ const sal_Char sAPI_drop_down[]                 = "DropDown";
 const sal_Char sAPI_header[]                    = "Header";
 const sal_Char sAPI_footer[]                    = "Footer";
 const sal_Char sAPI_datetime[]                  = "DateTime";
+const sal_Char sAPI_pagetitle[]                 = "PageTitle";
 
 // property names
 const sal_Char sAPI_is_fixed[]          = "IsFixed";