Remove override for integration test ESS region

[pchila]

What does this PR do?

Restore default ESS region for CI integration tests

Why is it important?

Overridden region azure-eastus2 seems to experience some difficulties at the moment. This should restore CI builds.
This is a temporary measure before we move to a more stable ESS environment (not qa, see #3459)

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 added an entry in ./changelog/fragments using the changelog tool
• [ ] I have added an integration test or an E2E test

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• Closes Revert ESS region change for integ test #3444

Use cases

Screenshots

Logs

Questions to ask yourself

• How are we going to support this in production?
• How are we going to measure its adoption?
• How are we going to debug this?
• What are the metrics I should take care of?
• ...

[mergify]

This pull request does not have a backport label. Could you fix it @pchila? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d./d is the label to automatically backport to the 8./d branch. /d is the digit

NOTE: backport-skip has been added to this pull request.

[cmacknz]

Hopefully this fixes things, thanks.

[elastic-sonarqube]

SonarQube Quality Gate

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
No Duplication information

[elasticmachine]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Start Time: 2023-09-28T13:18:06.782+0000

• Duration: 28 min 45 sec

Test stats 🧪

Test	Results
Failed	0
Passed	6313
Skipped	59
Total	6372

💚 Flaky test report

Tests succeeded.

🤖 GitHub comments

Expand to view the GitHub comments

To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

• /package : Generate the packages.

• run integration tests : Run the Elastic Agent Integration tests.

• run end-to-end tests : Generate the packages and run the E2E Tests.

• run elasticsearch-ci/docs : Re-trigger the docs validation. (use unformatted text in the comment!)

[elasticmachine]

🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	98.78% (81/82)	👍
Files	66.102% (195/295)	👍
Classes	65.693% (360/548)	👍
Methods	52.744% (1134/2150)	👍
Lines	38.131% (12854/33710)	👎 -0.024
Conditionals	100.0% (0/0)	💚