test_options: don't pass an old_options argument to options_validate()

This input was inessential, and none of the tests actually depended
on it or tested anything about it (as can be seen from the fact that
tests all still pass when it's removed).

I tried to generate this commit with a coccinelle script, but it had
trouble parsing a lot of options_validate as it stands.  Instead, I
did a search-and-replace to replace "tdata->old_opt," with "NULL,".