MNTOR-5092: Remove redesigned landing page

[Vinnl]

References:

Jira: MNTOR-5092
Figma:

Description

The redesigned landing page is no longer in use anywhere since the flag got turned off. Likewise, the page /subscription-plans/ already redirects to the landing page for everyone.

How to test

The removal went relatively smooth, with only a single change needed to the tests, and no linting errors, so I'm not sure if that makes me more or less confident 😅 In principle, all behaviour should be the same as before with the LandingPageRedesign flag off and FreeOnly on, like currently on production, in particular on the public (non-logged-in) pages.

Checklist (Definition of Done)

• Localization strings (if needed) have been added removed.
• Commits in this PR are minimal and have descriptive commit messages.
• I've added or updated the relevant sections in readme and/or code comments
• I've added a unit test to test for potential regressions of this bug. - Existing tests still succeed
• If this PR implements a feature flag or experimentation, I've checked that it still works with the flag both on, and with the flag off.
• If this PR implements a feature flag or experimentation, the Ship Behind Feature Flag status in Jira has been set
• Product Owner accepted the User Story (demo of functionality completed) or waived the privilege.
• All acceptance criteria are met. - Still need to remove FreeOnly
• Jira ticket has been updated (if needed) to match changes made during the development process.
• Jira ticket has been updated (if needed) with suggestions for QA when this PR is deployed to stage.