fix(server): cleanup import of the removed method (#3439)

This is a leftover from 5f13e11.

Author: devoto13

lib/server.js

@@ -22,7 +22,6 @@ const plugin = require('./plugin')
 const createServeFile = require('./web-server').createServeFile
 const createServeStaticFile = require('./web-server').createServeStaticFile
 const createFilesPromise = require('./web-server').createFilesPromise
-const createReadFilePromise = require('./web-server').createReadFilePromise
 const createWebServer = require('./web-server').createWebServer
 const preprocessor = require('./preprocessor')
 const Launcher = require('./launcher').Launcher
@@ -83,7 +82,6 @@ class Server extends KarmaEventEmitter {
       serveFile: ['factory', createServeFile],
       serveStaticFile: ['factory', createServeStaticFile],
       filesPromise: ['factory', createFilesPromise],
-      readFilePromise: ['factory', createReadFilePromise],
       socketServer: ['factory', createSocketIoServer],
       executor: ['factory', Executor.factory],
       // TODO(vojta): remove