Fix increased package size of public/assets

What does this MR do?

With https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/24542 gitlab:assets:compile started downloading public/assets from compile-assets. Both jobs run with different NODE_ENV leading to different build results:

• compile-assets does not run in production mode, leading to bigger, unoptimized chunks
• gitlab:assets:compile does run in production mode, splitting the chunks and optimizing them. If we now download the assets from compile-assets we end up with a lot of unused files, that bloat the images.

Relevant discussion: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/24542/diffs#note_136961260

What are the relevant issue numbers?

• Closes gitlab-org/distribution/team-tasks#310 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer