Remove implementation specific function name of EventDispatcher

[zyearn]

Some of the member functions of EventDispatcher are implementation specific, for example AddEpollOut.

We need to change that specific function name and adopt more general name then we can easily support brpc to more platforms.

[fansehep]

这里只需改变AddEpollOut 和 RemoveEpollOut 两个函数即可, AddEpollOut => AddMultiplex RemoveEpollOut => RemoveMultiplex 这种命名是否是一个合适的做法呢?

[Divyansh200102]

I want to work on this issue @zyearn

[Divyansh200102]

Please review this pr as well @zyearn