Use a different cookie to expire any cookies people may already have

We also check for a specific value in case people set it to `true` for some reason.

src/vector/index.js

@@ -272,7 +272,7 @@ async function loadApp() {
         const isIos = /iPad|iPhone|iPod/.test(navigator.userAgent) && !window.MSStream;
         const isAndroid = /Android/.test(navigator.userAgent);
         if (isIos || isAndroid) {
-            if (!document.cookie.split(';').some((c) => c.startsWith('mobile_redirect_to_guide'))) {
+            if (document.cookie.indexOf("riot_mobile_redirect_to_guide=false") === -1) {
                 window.location = "mobile_guide/";
                 return;
             }

src/vector/mobile_guide/index.js

@@ -2,7 +2,7 @@ import {getVectorConfig} from '../getconfig';
 
 function onBackToRiotClick() {
     // Cookie should expire in 4 hours
-    document.cookie = 'mobile_redirect_to_guide=false;path=/;max-age=14400';
+    document.cookie = 'riot_mobile_redirect_to_guide=false;path=/;max-age=14400';
     window.location.href = '../';
 }