wap_ldf audit does not work

I am not sure how auditing should work.
Unless someone (@hal3) knows how to fix it in wap_ldf, let's delete the unreachable code.
I am not even sure whether it is broken: `vw --wap_ldf=m --audit` gives me some audit info.

Why is the code unreachable?
feature_index is initiated to 0
v_array.size() is always >=0
Therefore, (ecsub->audit_features[*i].size() >= feature_index) is always true,
but the condition is negated,
so the deleted auditing code is never executed.
Therefore, ec->audit_features[wap_ldf_namespace] is empty and there is no need to clean it.

It seems the code was always unreachable since 2012 when it was commited.
https://github.com/JohnLangford/vowpal_wabbit/commit/0519e752b4521bb8a08b7b5b5bebeac32e3efb7f#diff-e8fdbe4c1b5c11940a5f5816c53d7524R307