math: Remove duplicate cos() declaration

Looks like we were registering cos() twice.

Author: RobLoach

include/chaiscript/extras/math.hpp

@@ -10,7 +10,6 @@ namespace chaiscript {
       template<typename Ret, typename Param>
       ModulePtr cos(ModulePtr m = std::make_shared<Module>())
       {
-        m->add(chaiscript::fun([](Param p){ return std::cos(p); }), "cos");
         m->add(chaiscript::fun([](Param p){ return std::cos(p); }), "cos");
         return m;
       }