Drop the spec in YamlProcessor that reads current .gitlab-ci.yml

What does this MR do?

Removes a spec.

Why was this MR needed?

In order to be able to use some licensed features, such as include in our .gitlab-ci.yml file, we need to supply a license. However, this spec only reads the current configuration file and checks if there are errors parsing it. If there were errors parsing the file however, CI wouldn't even run which makes this spec redundant. For this reason, it was discussed that we should at minimum remove the spec as it serves no purpose for the CI environment, and for the development environment it is better to set a fixture.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/48557