Remove inline JavaScript for Search autocomplete

## What does this MR do?

Remove inline JavaScript from the search partial for Search autocomplete.

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

That this doesn't break anything (it didn't when I tested it!)

## Why was this MR needed?

Inline scripts are bad, this removes a few of them.

## What are the relevant issue numbers?

#18231 and #19866

## Does this MR meet the acceptance criteria?

- Tests
  - [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5284