remove unused parameters from the plugin tab constructor

src/app/panels/righthand-panel.js

@@ -160,7 +160,7 @@ function RighthandPanel (appAPI, events, opts) {
 
   self.pluginManager = new PluginManager(appAPI, events)
   events.rhp.register('plugin-loadRequest', (json) => {
-    var content = pluginTab(optionViews, {}, {}, {}, json.url)
+    var content = pluginTab(optionViews, json.url)
     this._view.tabbedMenu.addTab(json.title, 'plugin', content)
     self.pluginManager.register(json, content)
   })

src/app/tabs/plugin-tab.js

@@ -1,7 +1,7 @@
 var yo = require('yo-yo')
 var css = require('./styles/plugin-tab-styles')
 
-function plugintab (container, appAPI, events, opts, url) {
+function plugintab (container, url) {
   var el = yo`
     <div class="${css.pluginTabView}" id="pluginView">
       <iframe class="${css.iframe}" src="${url}/index.html"></iframe>