Remove an unused routing helper for snippet emojis

What does this MR do?

This MR removes a GitlabRoutingHelper method that was unused, and it's associated tests.

The helper method is gitlab_toggle_award_emoji_snippet_url - I could not find any instance of it being used outside of the test suite.

This is a developer-facing change, so no changelog entry has been added.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.