Remove deprecated AWS config options

[kaiyan-sheng]

What does this PR do?

Remove default_region in aws module config: #13535
Remove aws_partition from AWS: #23590

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.next.asciidoc or CHANGELOG-developer.next.asciidoc.

[elasticmachine]

Pinging @elastic/integrations (Team:Integrations)

[mergify]

This pull request does not have a backport label. Could you fix it @kaiyan-sheng? 🙏
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 7./d branch. /d is the digit

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

[elasticmachine]

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Build stats

• Start Time: 2021-10-01T16:20:30.921+0000

• Duration: 127 min 56 sec

• Commit: efe3cb0

Test stats 🧪

Test	Results
Failed	0
Passed	24784
Skipped	1630
Total	26414

💚 Flaky test report

Tests succeeded.

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