test: simplify clearCache, drop logout helpers, simplify button selectors

- Drop `await clearCache()` from login/auth helpers; clearing cache before
  every login is no longer necessary now that charlie isolates sessions.
- Replace `logout` helpers with `clearCache` directly in `it()` calls; the
  helpers were either thin wrappers around `clearCache()` or did real
  navigation that is no longer worth the maintenance.
- Simplify `xpath=//button[text()=...]` / `[contains(., ...)]` button text
  selectors to charlie's bare-string (or RegExp for OR-clauses) form.

test/test.js

@@ -1,6 +1,6 @@
 #!/usr/bin/env node
 
-import { app, click, cloudronCli, goto, loginOIDC, sendKeys, setupBrowser, takeScreenshot, teardownBrowser, waitFor } from '@cloudron/charlie';
+import { app, clearCache, click, cloudronCli, goto, loginOIDC, sendKeys, setupBrowser, takeScreenshot, teardownBrowser, waitFor } from '@cloudron/charlie';
 
 /* global it, describe, before, after, afterEach */
 
@@ -32,12 +32,6 @@ describe('Application life cycle test', function () {
         await loginOIDC('xpath=//span[contains(., "Bookmarks")] | //strong[text()="Successfully authenticated from Cloudron account."]');
     }
 
-    async function logout() {
-        await goto(`https://${app.fqdn}/settings/preferences/appearance`, 'css=#logout');
-        await click('css=#logout');
-        await waitFor('css=#user_email');
-    }
-
     async function checkTimeline() {
         await goto(`https://${app.fqdn}/home`, 'Your home timeline is empty');
     }
@@ -70,7 +64,7 @@ describe('Application life cycle test', function () {
     it('registration is disabled', checkRegistrationClosed);
     it('can OIDC login', loginOidc);
     it('can see timeline', checkTimeline);
-    it('can logout', logout);
+    it('can logout', clearCache);
 
     it('backup app', cloudronCli.createBackup);
     it('restore app', cloudronCli.restoreFromLatestBackup);
@@ -91,7 +85,7 @@ describe('Application life cycle test', function () {
     // test update
     it('can install app for update', cloudronCli.appstoreInstall);
     it('can OIDC login', loginOidc);
-    it('can logout', logout);
+    it('can logout', clearCache);
 
     it('can update', cloudronCli.update);