Remove demo code

[mathemancer]

Fixes #3531

This PR removes all Demo code which is otherwise unused from Mathesar.

Technical details

Some demo code was used for example datasets in other context, and so was moved to a different location rather than removed entirely.

Checklist

- [X] My pull request has a descriptive title (not a vague title like `Update index.md`). - [X] My pull request targets the `develop` branch of the repository - [X] My commit messages follow [best practices][best_practices]. - [X] My code follows the established code style of the repository. - [ ] I added tests for the changes I made (if applicable). - [X] I added or updated documentation (if applicable). - [X] I tried running the project locally and verified that there are no visible errors. [best_practices]:https://gist.github.com/robertpainsi/b632364184e70900af4ab688decf6f53 ## Developer Certificate of Origin

Developer Certificate of Origin

``` Developer Certificate of Origin Version 1.1 Copyright (C) 2004, 2006 The Linux Foundation and its contributors. 1 Letterman Drive Suite D4700 San Francisco, CA, 94129 Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. Developer's Certificate of Origin 1.1 By making a contribution to this project, I certify that: (a) The contribution was created in whole or in part by me and I have the right to submit it under the open source license indicated in the file; or (b) The contribution is based upon previous work that, to the best of my knowledge, is covered under an appropriate open source license and I have the right under that license to submit that work with modifications, whether created in whole or in part by me, under the same open source license (unless I am permitted to submit under a different license), as indicated in the file; or (c) The contribution was provided directly to me by some other person who certified (a), (b) or (c) and I have not modified it. (d) I understand and agree that this project and the contribution are public and that a record of the contribution (including all personal information I submit with it, including my sign-off) is maintained indefinitely and may be redistributed consistent with this project or the open source license(s) involved. ```

[kgodey]

I assume we want to wait until the April release branch is cut (cc @ghislaineguerin) before we merge this.

[mathemancer]

I assume we want to wait until the April release branch is cut (cc @ghislaineguerin) before we merge this.

Definitely.

@pavish Any opinions on whether we should remove the demo-mode-related translations? I know we paid for them, but we can always recover them through git or other means when/if we want them back.

[pavish]

@mathemancer

Any opinions on whether we should remove the demo-mode-related translations? I know we paid for them, but we can always recover them through git or other means when/if we want them back.

Yes, we should remove any key we're no longer using. We can always recover them if needed, Transifex also has a memory feature for previously translated strings, apart from git.

[kgodey]

Agreed that paying for the translations isn't a reason to keep them around if we no longer need them.

[mathemancer]

Okay, this is now ready for review. From @pavish , I'm just requesting a quick check to make sure there aren't any obvious problems where the front end might break because it expects something (e.g., a flag or variable) to be available from the back end.

[ghislaineguerin]

@kgodey @mathemancer I have cut the release 2 days ago.

[mathemancer]

@pavish I made the requested change.

[Anish9901]

Waiting on your re-review @pavish, please merge this if you don't have any more concerns.