remove unneeded dTHX's
Revert "remove unneeded dTHX's"

This reverts commit eafb9822635b31c472348fb9b796382ab8584cdb.
use PERL_UNUSED_ARG(my_perl) to silence gcc warning under Win7/x64
Merge pull request #105 from rns/gcc_win64_warnings

remove unneeded dTHX's