Remove file content QA selector from simple viewer

What does this MR do?

Removes duplicated file_content selector for create snippet tests

Hopefully resolve gitlab-com/gl-infra/production#4121 (closed) and #326454 (closed)

Related to !57705 (diffs)

Original commit removed from blob viewer, however ./qa/specs/features/browser_ui/3_create/snippet/create_project_snippet_spec.rb used this and failed. The second commit removes the selector from the simple viewer instead.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
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Related to #4121 (closed)