[Ingest Manager] Refactor: remove deadcode

[michalpristas]

What does this PR do?

Removes deadcode and fixes some issues raised by static check.

Why is it important?

Readability

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/agent (Team:Agent)

[elasticmachine]

Pinging @elastic/ingest-management (Team:Ingest Management)

[botelastic]

This pull request doesn't have a Team:<team> label.

[blakerouse]

I like all the RED!

[elasticmachine]

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Build stats

• Build Cause: Pull request #24715 opened

• Start Time: 2021-03-23T17:41:51.776+0000

• Duration: 52 min 4 sec

• Commit: 8647315

Test stats 🧪

Test	Results
Failed	0
Passed	6588
Skipped	16
Total	6604

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Test stats 🧪

Test	Results
Failed	0
Passed	6588
Skipped	16
Total	6604

[michalpristas]

/package