Try removing passport.session in LINE notify OAuth2 process

[MrOrz]

Actually we don't need to store "user" in session. We are not authenticating user anyway, we just get a token in a one-time OAuth2 process and then store it to database.

passport.session(), passport.serializeUser and passport.deserializeUser are used to store "user" in session. I think after removing these together, LINE notify would still work?

Originally posted by @MrOrz in #185