Revert "Merge branch '4097-branch-is-no-longer-checked-out-when-using-refspec' into 'master'"

What does this MR do?

Revert the fix for missing branch: #4097 (comment 156508723).

The reasons for doing that:

1. The feature never worked as intended,
2. It worked by only for default_branch because we did git clone,
3. If git fetch is used, the default_branch is never updated,
4. None of other branches is accessible using local reference.
5. This adds severe performance regression: git fetch from remote source, for GitLab EE it adds at least 3.3MB of extra traffic for each CI job.

curl 'https://gitlab.com/gitlab-org/gitlab-ee.git/info/refs?service=git-upload-pack' > /dev/null

The fix is simple if done from .gitlab-ci.yml:

script: git push -f heroku HEAD:master

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Added tests for this feature/bug
• In case of conflicts with master - branch was rebased

What are the relevant issue numbers?

Related to #4097 (closed)