Merge branch 'remove-unused-templates-from-gitlab-ci' into 'master'

Clean up some unused templates imported from GitLab CI

## What does this MR do?

Clean up some unused templates imported from GitLab CI, for new developers to easily understand the file/directory structure of Gitlab CE.

## Are there points in the code the reviewer needs to double check?

Be sure if removed files are not used now while the committer checked them once.

## Why was this MR needed?

Because the file/directory structure of the repository should be clear and simple and if so new developers can easily understand the file/directory structure of Gitlab CE.

## What are the relevant issue numbers?

Closes #19158 

## Does this MR meet the acceptance criteria?

- CHANGELOG won't be updated due to repository maintenance
- No documentation created/updated
- No API support added
- Tests
  - [skipped] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !4922