Fix Prometheus duplicate metrics

What does this MR do?

Stop duplicate 0 metrics from appearing on the /-/metrics endpoint for http_request_duration_seconds

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

I'm unsure if this will affect performance

• [-] Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers

Security