Merge branch 'use-let-in-tests' into 'master'

Use user from let instead recreate in before

## What does this MR do?
It`s minor fix in tests. We can use factory from let instead recreate user before each test.
 
## Are there points in the code the reviewer needs to double check?
No

## Why was this MR needed?

## Screenshots (if relevant)
No

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [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 it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

See merge request !6762

spec/controllers/projects/blob_controller_spec.rb

@@ -5,7 +5,6 @@ describe Projects::BlobController do
   let(:user)    { create(:user) }
 
   before do
-    user = create(:user)
     project.team << [user, :master]
 
     sign_in(user)