messagegui: fixes and memory optimisation for Bangle.js 1

Don't add widget utils as it's currently broken for Bangle.js 1 (keeps
widget utils for Bangle.js 2).

Delete some variables before trying to navigate to a message overview
from the messages scroller.

Author: thyttan

apps/messagegui/app.js

@@ -287,8 +287,8 @@ function showMessagesScroller(msg) {
   if (replying) { return; }
   active = "scroller";
 
-  const WU = require("widget_utils");
-  WU.hide();
+  const WU = 1!==process.env.HWVERSION ? require("widget_utils") : undefined;
+  WU&&WU.hide();
   const APP_RECT = Bangle.appRect;
 
   var bodyFont = fontBig;
@@ -340,7 +340,8 @@ function showMessagesScroller(msg) {
       for (let i=firstTitleLinePerMsg.length-1; i>=0 ; i--) {
         if (scrollIdx>=firstTitleLinePerMsg[i]) {
           if (!touch || touch.type===0) {
-            WU.show();
+            WU&&WU.show();
+            delete titleLines, allLines;
             showMessageRouter(MESSAGES[i], true, "overview");
             updateReadMessages();
           }