...as the implicitly defined copy operations would just copy the m_p* member
pointers. Needed some modification of the ParserCleanup class so that Entity
(which has a XMLFile2UTFConverter member) can be std::move'd into
Found by new -Wdeprecated-copy of GCC trunk towards GCC 9.
Reviewed-by: Stephan Bergmann <firstname.lastname@example.org>