Update to the edx-platform Preview Functionality

[feanil]

We recently merged openedx/openedx-platform#36460 into edx-platform which removed the last vestiges of the old preview functionality. The learning MFE now supports preview capability without needing a second subdomain. The settings related to that domain have been removed from edx-platform and probably need to be removed from Tutor as well.

[Danyal-Faheem]

The PR to resolve this issue have been merged into the main branch.

The teak branch was later on rebased on top of main and the sandbox was re-initialized, only to find out that the upstream preview page removal change was never meant to be backported to teak. For this reason, the commits have been reverted from the teak branch and will now only exist in the main branch until the upstream changes are merged into a release.

[DawoudSheraz]

Adding to the above, we will need to re-create new PRs for main once teak branch is merged because teak will merge to release, which will then merge back to main, and the preview changes won't be active.