Revert "fix(socketio/socket): create a different socket id for each ns"

[Totodore]

Reverts #123

It appears that solving this issue implies a big refactoring. Indeed referencing socketio socket with custom sid instead is impossible because of the following architecture :
client recv data from engine socket -> route to corresponding namespace -> route to corresponding socket with <Engine id -> socket> hashmap

Because the socket id is not in the request it is impossible to map socket by their socket id (and not their engine id).
The solution would be to refactor the code to match the official architecture :
client wraps an engine socket and holds a map of the ns -> socket.