Fix logstash integration with monitoring

[joshdover]

Summary

The monitoringUiEnabled injected var was removed and broke the Logstash plugin's integration with Monitoring. This PR changes that check to simply look to see if the monitoring plugin is enabled at all.

Checklist

Delete any items that are not applicable to this PR.

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• This was checked for keyboard-only and screenreader accessibility
• This renders correctly on smaller devices using a responsive layout. (You can test this in your browser
• This was checked for cross-browser compatibility, including a check against IE11

For maintainers

• This was checked for breaking API changes and was labeled appropriately

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Pinging @elastic/kibana-platform (Team:Platform)

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 18c90a6

History

• 💔 Build #45227 failed 12b88cb

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[joshdover]

@elasticmachine merge upstream

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