Fix unused parameter warnings

I always compile with -Wall and friends, so when something gets a warning that is easy to fix, I always try to fix it.

Some of the parameters are unused,  and the best way to silence the warning is to remove the parameter name, which is what this patch does. Something I wasn't sure of was the removal of the `attr` parameter, which defaulted to a default constructed `std::string` but it was used nowhere.

The main reason why warnings can be annoying or cumbersome is due to the fact that some people (such as myself) compile with -Werror and treat all warnings as errors.