Remove obsolete SAL_FALLTHROUGH completely

...after 7ffdd830d5
"HAVE_CPP_ATTRIBUTE_FALLTHROUGH is always true now"

Change-Id: I54e5ff4e036a6bb3e5774d1c0524158aae18e937
Reviewed-on: https://gerrit.libreoffice.org/64800
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

cppu/source/typelib/typelib.cxx

@@ -1285,7 +1285,7 @@ static void typelib_typedescription_destructExtendedMembers(
     case typelib_TypeClass_STRUCT:
         delete[] reinterpret_cast< typelib_StructTypeDescription * >(pTD)->
             pParameterizedTypes;
-        SAL_FALLTHROUGH;
+        [[fallthrough]];
     case typelib_TypeClass_EXCEPTION:
     {
         typelib_CompoundTypeDescription * pCTD = reinterpret_cast<typelib_CompoundTypeDescription*>(pTD);