Deprecate pre-redesign settings page

[flozia]

References:

Jira: MNTOR-3828

Description

Removes the pre-redesign settings page including:

• feature flag SettingsPageRedesign
• old settings page view
• deprecated components
• deprecated styling
• duplicate unit tests

How to test

1. The feature flag SettingsPageRedesign should not be listed anymore
2. Visiting the settings page /user/settings should not result in any visible issues
   1. Edit your info: /settings/edit-info
   2. Set notifications: /settings/notifications
   3. Manage account: /settings/manage-account

Checklist

• Commits in this PR are minimal and have descriptive commit messages.
• I've added a unit test to test for potential regressions of this bug.
• 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.
• All acceptance criteria are met.
• Jira ticket has been updated with suggestions for QA when this PR is deployed to stage.

[github-actions]

Preview URL 🚀 : https://blurts-server-pr-5520-mgjlpikfea-uk.a.run.app

[github-actions]

Cleanup completed - database 'blurts-server-pr-5520' destroyed, cloud run service 'blurts-server-pr-5520' destroyed