fix: do not emit "error" events

[darrachequesne]

Forcing users to handle "error" events is useless since there is no
interesting way to handle them (no retry, for example).

Before:

io.adapter(createAdapter(pool));

poll.on("error", (err) => {
  // client disconnection
});

io.of("/").adapter.on("error", () => {
  // needed so that no exception is thrown
});

After:

io.adapter(createAdapter(pool));

poll.on("error", (err) => {
  // client disconnection
})

[darrachequesne]

Superseded by ec1b78c.