fix: use staging env for package registry

[mdelapenya]

What does this PR do?

It uses the staging environment of EPR, as it contains the system package in 7.16

FOr the elastic-package provider, we are removing the package-registry service from the startup list.

Why is it important?

Keep consistent and clean deployments, without using the local package registry at all.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have run the Unit tests (make unit-test), and they are passing locally
• I have run the End-2-End tests for the suite I'm working on, and they are passing locally
• I have noticed new Go dependencies (run make notice in the proper directory)

Related issues

• Relates Use elastic-package again #1737

[mdelapenya]

Merging, as ARM test suite started to go green again

[elasticmachine]

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Build stats

• Start Time: 2021-11-02T12:13:57.751+0000

• Duration: 49 min 24 sec

• Commit: 2eb9a74

Test stats 🧪

Test	Results
Failed	0
Passed	242
Skipped	0
Total	242

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