Fix syntax error in initializers/fill_shards

What does this MR do?

Remove return statement from an initializer. Otherwise, I receive SyntaxError on many rake tasks.

rake aborted!
SyntaxError: /Users/dzaporozhets/Projects/gitlab-development-kit/gitlab/config/initializers/fill_shards.rb:1: Invalid return
/Users/dzaporozhets/Projects/gitlab-development-kit/gitlab/config/initializers/fill_shards.rb:2: Invalid return
/Users/dzaporozhets/Projects/gitlab-development-kit/gitlab/config/initializers/fill_shards.rb

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• 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.