hashtable: Avoid use of std::unary_function
It is removed by C++17. It only defines some typedef members for derived functionals. We don't use those, so just drop it.
System updates will be applied on January 22st between 0900 AM and 1200 PM, EST (UTC-05:00). This site may have intermittent downtime during that time.
It is removed by C++17. It only defines some typedef members for derived functionals. We don't use those, so just drop it.