Revert workaround for missing fleet.hosts

[axw]

Motivation/summary

This is no longer needed, with elastic/elastic-agent#1802, and it triggers a panic in ESS after upgrading from 7.x deployments.

Checklist

- [ ] Update CHANGELOG.asciidoc
- [ ] Update package changelog.yml (only if changes to apmpackage have been made)
- [ ] Documentation has been updated

How to test these changes

1. Create a 7.17.x ESS deployment
2. Upgrade to 8.6
3. Make sure APM Server comes up and is accessible

Related issues

None

[apmmachine]

💚 Build Succeeded

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Build stats

• Start Time: 2022-12-07T13:45:37.821+0000

• Duration: 28 min 1 sec

Test stats 🧪

Test	Results
Failed	0
Passed	153
Skipped	0
Total	153

🤖 GitHub comments

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[lahsivjar]

Confirmed that APM-Server is healthy on upgrade from 7.17.8 to 8.6.0-BC6 and is accepting requests.