Resolve "Do not pre-select previous user(s) when creating protected branches"

What does this MR do?

Plan: https://gitlab.com/snippets/1722521

Removes the local storage read/write logic from protected_branch_create.js to stop it setting a user by default.

It also removes this logic from the CE scoped protected_branch_create because it's not available in CE.

CE port: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/19714

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

If you set up a protected branch with a user, when visiting a different project and setting up a protected branch, the previous user will be selected by default, even if they're not in the project, and they can be very far down the list to deselect.

Screenshots (if relevant)

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
• EE specific content should be in the top level /ee folder
• 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
• If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

Closes #6407 (closed)