use_elasticsearch? should not rely upon params

The following discussion from !112244 (merged) should be addressed:

• @terrichu started a discussion: (+1 comment)

  @tbulva tested this locally and it works great. I found one edge case but I'm not sure it should be fixed in this MR. Specifically when typing in scope=epics&project_id=XX into the URL, the backend search falls back to Basic search. This is due to the use_elasticsearch? check using params[:scope] instead of the scope set in the search_service. I'd rather open a follow up issue to look into refactoring this. wdyt?

  example url: http://gdk.test:3000/search?search=test&scope=epics&project_id=7

  Notice there is no "Advanced Search" seen in the corner