Don't start key backups when opening settings (#11640)

* SecureBackupPanel: stop calling `checkKeyBackup`

`checkKeyBackup` will start key backups if they aren't already running. In my
not-so-humble opinion, the mere act of opening a settings panel shouldn't change anything.

* fix SecurityUserSettingsTab test

test/components/views/settings/tabs/user/SecurityUserSettingsTab-test.tsx

@@ -41,6 +41,7 @@ describe("<SecurityUserSettingsTab />", () => {
         ...mockClientMethodsCrypto(),
         getRooms: jest.fn().mockReturnValue([]),
         getIgnoredUsers: jest.fn(),
+        getKeyBackupVersion: jest.fn(),
     });
 
     const getComponent = () => (