use existing translation for subscribe button instead of custom key

customize.dist/pages.js

@@ -181,11 +181,11 @@ define([
 
     Pages.subscribeButton = function (onClick) {
         var _link = h('a', {
-            href: "/accounts/",
+            href: AppConfig.upgradeURL || "/accounts/",
         });
 
         var subscribe = h('button', [
-            Msg.subscribe_button
+            Msg.features_f_subscribe,
         ]);
 
         $(subscribe).click(function () {

customize.dist/pages/index.js

@@ -74,7 +74,7 @@ define([
 
         var subscribeButton;
         /* Display a subscribe button if they are enabled and the button's translation key exists */
-        if (Config.allowSubscriptions && Msg.subscribe_button) {
+        if (Config.allowSubscriptions) {
             subscribeButton = Pages.subscribeButton(function () {
                 Feedback.send('HOME_SUBSCRIBE_CRYPTPAD');
             });