Remove static JavaScript HAML fixtures

What does this MR do?

Replaces the static HAML fixtures used in frontend tests with static HTML files. This reduces the running time of bin/rake karma:fixtures by almost 50% (from 90 seconds to 50 seconds).

What are the relevant issue numbers?

part of https://gitlab.com/gitlab-org/gitlab-ce/issues/49127

closes https://gitlab.com/gitlab-org/gitlab-ce/issues/24753

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