Remove redundant ws dependency

`socket.io` already depends on `ws` and uses it by default.
The separate dependency to and initialization of `ws` sees to be
a relic of the past usage of `uws`, but is redundant now.

As documented in https://socket.io/docs/v2/server-initialization/#Notable-options,
`perMessageDeflate` is now `false` by default.

Signed-off-by: David Mehren <git@herrmehren.de>

app.js

@@ -74,10 +74,6 @@ metrics.setupCustomPrometheusMetrics()
 
 // socket io
 const io = require('socket.io')(server, { cookie: false })
-io.engine.ws = new (require('ws').Server)({
-  noServer: true,
-  perMessageDeflate: false
-})
 
 // others
 const realtime = require('./lib/realtime.js')