Remove download of tar files

I think it's useful to be able to get to the tarballs somehow, for example github allows you to get zips and tarballs of tags https://github.com/drupal/core/tags

The main issue is that the tarballs/zip are quite prominent and listed as 'Alternative installation files', if we could just quietly list the tar.gz and zip without mentioning installation, that would be good.

The 'Drupal 8 or later' messaging should go when Drupal 7 support is dropped, it's not great that a lot of documentation and user interface elements reference a release that's been out of support for two years, even if we all know that means 'modern Drupal' a lot of people won't.

Tried to expand the issue title a bit.

Also not entirely sure we need to postpone this if we don't entirely remove the links, so moving to 'active'.

With the Drupal.org rebranding work, there were too many things like CTAs on https://www.drupal.org/download → , and the tgz & zip download links got removed.

Core and contrib release pages do have some differences, so the proposed changes for each should be clearly summarized.

Drupal doesn't really support directly downloading a tarball any more, but release pages still show .tar.gz and .zip and 'Alternative installation files'.

This is true for contrib. And mostly true for core - the results of composer create-project and extracting the archive are the same. Using Composer to create the project is a good way to make sure composer is present and working from the start.

Composer still relies on the same .tar.gz files that d.o publishes so we're not actually removing them as such.

This is totally true for contrib (technically, Composer only uses .zip files, not .tar.gz). Composer does not use the core zip files.