ref(invite): remove unused nuclear-js dep (#2642)

package-lock.json

       "resolved": "https://registry.npmjs.org/image-size/-/image-size-0.6.2.tgz",
       "integrity": "sha512-pH3vDzpczdsKHdZ9xxR3O46unSjisgVx0IImay7Zz2EdhRVbCkj+nthx9OuuWEhakx9FAO+fNVGrF0rZ2oMOvw=="
     },
-    "immutable": {
-      "version": "3.8.2",
-      "resolved": "https://registry.npmjs.org/immutable/-/immutable-3.8.2.tgz",
-      "integrity": "sha1-wkOZUUVbs5kT2vKBN28VMOEErfM="
-    },
     "import-local": {
       "version": "0.1.1",
       "resolved": "https://registry.npmjs.org/import-local/-/import-local-0.1.1.tgz",
         "gauge": "1.2.7"
       }
     },
-    "nuclear-js": {
-      "version": "1.4.0",
-      "resolved": "https://registry.npmjs.org/nuclear-js/-/nuclear-js-1.4.0.tgz",
-      "integrity": "sha1-bJwAGwZz8K6dj4sYjE2gTtaTp74=",
-      "requires": {
-        "immutable": "3.8.2"
-      }
-    },
     "num2fraction": {
       "version": "1.2.2",
       "resolved": "https://registry.npmjs.org/num2fraction/-/num2fraction-1.2.2.tgz",

package.json

     "lib-jitsi-meet": "github:jitsi/lib-jitsi-meet#0503ec4d3f175b154b1c6fd7037520ce0768fa58",
     "lodash": "4.17.4",
     "moment": "2.19.4",
-    "nuclear-js": "1.4.0",
     "postis": "2.2.0",
     "prop-types": "15.6.0",
     "react": "16.2.0",

react/features/invite/components/AddPeopleDialog.web.js

 
 import Avatar from '@atlaskit/avatar';
 import InlineMessage from '@atlaskit/inline-message';
-import { Immutable } from 'nuclear-js';
 import PropTypes from 'prop-types';
 import React, { Component } from 'react';
 import { connect } from 'react-redux';
          */
         addToCallInProgress: false,
 
-
-        // FIXME: Remove usage of Immutable. {@code MultiSelectAutocomplete}
-        // will default to having its internal implementation use a plain array
-        // if no {@link defaultValue} is passed in. As such is the case, this
-        // instance of Immutable.List gets overridden with an array on the first
-        // search.
         /**
          * The list of invite items.
          */
-        inviteItems: new Immutable.List()
+        inviteItems: []
     };
 
     /**

react/features/invite/functions.js

         inviteServiceUrl: string,
         inviteUrl: string,
         jwt: string,
-        inviteItems: Object): Promise<void> {
+        inviteItems: Array<Object>): Promise<void> {
     if (!inviteItems || inviteItems.length === 0) {
         return Promise.resolve();
     }