(Part 5) FE multiple approval rules - pipeline clean up

What does this MR do?

This MR fixes some issues with the feature branch https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9001.

• Removes ee/api.js file that was added to the feature branch.
• Renames references of the feature flag approval_rule to approval_rules (BE already updated this).
• Adds some sync: false to failing specs that use vue-test-utils.

PLEASE NOTE:

• This does not point to master.
• This will not fix the karma job on it's own. https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9433 needs to be merged with master to do that.

What are the relevant issue numbers?

• Part of #1979 (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.
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?
• Security reports checked/validated by reviewer