Unhandled promise rejection in socket client

[w33ble]

Kibana version: 6.6+

Browser version: Chrome latest

Describe the bug:

The socket is failing for the following error:

TypeError: Cannot read property 'emit' of null

It seems to happen when the socket connection dies and reconnects. The error is coming from kbn-interpreter.

I think it just needs to tear down the error listeners once the connect event happens.

Steps to reproduce:

1. Load Canvas
2. Restart the server
3. See error in browser console once the server is up

Screenshots (if relevant):

[elasticmachine]

Pinging @elastic/kibana-app