Use Elixir OTP wrappers instead of Erlang interfaces, remove unused alias warning

* Replace `:supervisor.start_link/2` with `Supervisor.start_link/2` in `Phoenix.Supervisor.start_link`
* Replace `:supervisor.start_link/4` with `Supervisor.start_link/3` in `Phoenix.Topic.Supervisor.start_link`
* Replace `:gen_server.call/2` with `GenServer.call/2` in `Phoenix.Topic.call/1`
* Replace `:gen_server.start_link/3` with `GenServer.start_link/3` in `Phoenix.Topic.Server.start_link`
* Remove unused alias of `Phoenix.Router.OptionsTest.PhoenixOptionsTest` that was causing warning on test suite runs